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{{Short description|Symbol placed before units of digital information to indicate multiplication by a power of two}}
In computing, '''binary prefixes''' are names or associated symbols that can precede a unit of measure (such as a ]) to indicate multiplication by a power of two. In certain contexts in computing (such as ] sizes), it is convenient to express large quantities in terms of multiples of the unit by powers of two.
{{About|powers-of-two prefixes for measurement units like bit and byte|notations for the radix of a numeral|Integer literal#Affixes}}
{{Use dmy dates|date=May 2019|cs1-dates=y}}
{{Redirect|Gibi|other uses|Gibi (disambiguation)}}


{{Bit and byte prefixes}}
As the binary multipliers 1,024 (2<sup>10</sup>), 1,048,576 (2<sup>20</sup>) (etc.) are close to certain ] such as kilo- (1000 = 10<sup>3</sup>) and mega- (1,000,000 = 10<sup>6</sup>) respectively, it has been traditional in some settings to use these prefixes for the binary meanings, that is, to use "mega" (or the symbol, M) to mean 1,048,576 instead of 1,000,000 and so on. However, these prefixes have the decimal meanings in every other context, e.g., when used with ]. Further, certain areas of computing have always used these prefixes to mean decimal multipliers, and not in the binary sense (e.g. when specifying quantities of individual bits on a ] ].) This has led to ambiguity on what these prefixes mean.<ref name="NIST"/>


A '''binary prefix''' is a ] that indicates a ] of a ] by an integer ]. The most commonly used binary prefixes are '''kibi''' (symbol Ki, meaning {{nowrap|1=2<sup>10</sup> = 1024}}), '''mebi''' ({{nowrap|1=Mi, 2<sup>20</sup> = {{val|1048576}}}}), and '''gibi''' ({{nowrap|1=Gi, 2<sup>30</sup> = {{val|1073741824}}}}). They are most often used in ] as multipliers of ] and ], when expressing the capacity of ]s or the size of computer ].
In an attempt to resolve this confusion, standards organisations have proposed a new set of binary prefixes to indicate binary multipliers. Each successive prefix is 1,024 (2<sup>10</sup>) times the previous one, rather than the 1,000 (10<sup>3</sup>) used by the ] system. The binary prefixes are being adopted slowly. National and international standards now state that the SI prefixes always refer to powers of ten, ''even in the context of information technology''.<ref name="NIST"/><ref name="BIPM"/><ref name="IEEE1541"/><ref name=ieee260>{{cite book|isbn=073813998X|title=IEEE Std 260.1-2004, IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units)|version=Revision of 260.1-1993|publisher=]|url=http://ieeexplore.ieee.org/servlet/opac?punumber=9287|date=] ]}}</ref> Nevertheless, the use of the SI prefixes as binary multipliers is still common in some areas: a standards group for the semiconductor device engineering industry, the ], defines "prefix to units of semiconductor storage capacity" using powers of two, clarifying in a note that the binary definitions are included "only to reflect common usage".<ref name="JEDEC"/>


The binary prefixes "kibi", "mebi", etc. were defined in 1999 by the ] (IEC), in the ] ] (Amendment 2). They were meant to replace the ] ] prefixes, such as "kilo" ({{nowrap|1=k, 10<sup>3</sup> = 1000}}), "mega" ({{nowrap|1=M, 10<sup>6</sup> = {{val|1000000}}}}) and "giga" ({{nowrap|1=G, 10<sup>9</sup> = {{val|1000000000}}}}),<ref name="BIPM8" /> that were commonly used in the computer industry to indicate the nearest powers of two. For example, a memory module whose capacity was specified by the manufacturer as "2&nbsp;megabytes" or "2&nbsp;MB" would hold {{nowrap|2 × 2<sup>20</sup>}} = {{nowrap|{{val|2097152}} bytes}}, instead of {{nowrap|2 × 10<sup>6</sup>}} = {{val|2000000}}.
== History ==
{{seealso|Timeline of binary prefixes}}
Early computers used one of two addressing methods to access the system memory; binary (base-2) or decimal (base-10). For instance, the ] (1952) used binary and could address 2,048 36-] ], while the ] (1953) used decimal and could address 10,000 7-bit words.

By the mid 1960s, binary addressing had become the standard architecture in computer design. The computer system documentation would specify the memory size with an exact number such as 32,768, 65,536 or 131,072 words of storage (all ]). There were several methods used to abbreviate these quantities. The use of ''K'' either in the binary or the decimal sense as in a "32K store" can be found as early as 1960.<ref>{{cite journal | last =Gruenberger | first =Fred | title =Letters to the Editor | journal =Communications of the ACM | volume =3 | issue =10 | date =October 1960 | url = http://doi.acm.org/10.1145/367415.367419 | doi = 10.1145/367415.367419 <!--//Retrieved from url by DOI bot-->}} "The 8K core stores were getting fairly common in this country in 1954. The 32K store started mass production in 1956; it is the standard now for large machines and at least 200 machines of the size (or its equivalent in the character addressable machines) are in existence today (and at least 100 were in existence in mid-1959)." Note: The IBM 1401 was a character addressable computer.</ref> ] seminal 1964 article on ] used 1K to mean 1024.<ref name="IBM360">{{cite journal | last =Amdahl | first = Gene M. | authorlink = Gene Amdahl | coauthors = ]; ]| title = Architecture of the IBM System/360 | journal =IBM Journal of Research and Development | volume =8 | issue =2 | publisher = IBM | date = 1964 | url = http://www.research.ibm.com/journal/rd/441/amdahl.pdf}} Figure 1 gives storage (memory) capacity ranges of the various models in "Capacity 8 bit bytes, 1 K = 1024"</ref> This style was used by other computer vendors, the ] ''System Description'' (1968) made extensive use of K as 1024.<ref name = "CDC7600">{{cite book | author = Control Data Corporation | title = Control Data 7600 Computer System: Preliminary System Description | year = November 1968 | url = http://archive.computerhistory.org/resources/text/CDC/CDC.7600.1968.102646087.pdf |quote = One type, designated as the small core memory (SCM) is a many bank coincident current type memory with a total of 64K words of 60 bit length (K=1024).}}</ref> Another style was to truncate the last 3 digits and append K. The exact values 32,768, 65,536 and 131,072 would then become 32K, 65K and 131K.<ref name = "CDC6600">{{cite book | author = Control Data Corporation | title = Control Data 6400/6500/6600 Computer Systems Reference Manual | year = 1965-1967 | pages = pg 2-1 | edition = Pub No. 60100000 | url = http://ed-thelen.org/comp-hist/CDC-6600-R-M.html#TOC/ |quote = Central Memory is organized into 32K, 65K, or 131K words (60-bit) in 8, 16, or 32 banks of 4096 words each.}}</ref> (If 32,768 were instead rounded off, it would be 33K; if K = 1024 were used, 65,536 would become "64K".) This style was used from about 1965 to 1975.

These two styles (K = 1024 and truncation) were used loosely around the same time, sometimes by the same company. (In discussions of binary-addressed memories, the exact size was evident from context.) The ] real-time computer (1974) denoted 196,608 as 196K and 1,048,576 as 1 M,<ref name "HP21MX">{{cite journal | last =Frankenberg | first =Robert | title =All Semiconductor Memory Selected for New Minicomputer Series | journal = Hewlett-Packard Journal | volume =26 | issue =2 | pages = pg 15–20 | publisher = Hewlett-Packard | date = October 1974 | url = http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1974-10.pdf | accessdate = 2007-06-18 | quote = 196K-word memory size}}</ref> while the ] business computer (1973) could have 64K, 96K, or 128K bytes of memory.<ref "HP3000"> {{Citation | last = Hewlett-Packard | title =HP 3000 Configuration Guide | journal = HP 3000 Computer System and Subsystem Data | pages = pg 59 | date = November 1973 | url = http://www.bitsavers.org/pdf/hp/3000/hp3000/5952-4500_optionsBrochure_Nov73.pdf}}</ref>

The terms Kbit, Kbyte, Mbit and Mbyte started to be used as binary units in the early 1970s.<ref name= "Mbyte1972"> {{cite journal | last = Lin | first = Yeong | coauthors = Mattson, Richard | title = Cost-performance evaluation of memory hierarchies | journal = Magnetics, IEEE Transactions on | volume =8 | issue =3 | pages = pg 390–392 | publisher = IEEE | date =September 1972 | url = http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=1067329&isnumber=22917 |quote = Also, random access devices are advantageous over serial access devices for backing store applications only when the memory capacity is less than 1 Mbyte. For capacities of 4 Mbyte and 16 Mbyte serial access stores with shift register lengths of 256 bit and 1024 bit, respectively, look favorable.}}</ref> Most memory capacities were expressed in K, even when M could have been used: The IBM System/370 Model 158 brochure (1972) had the following: "Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes."<ref name="IBM370">{{cite journal | last =IBM| title = System/370 Model 158 brochure | publisher = IBM | date = 1972 | url = http://archive.computerhistory.org/resources/text/IBM/IBM.370Mod158.1972.102646258.pdf | quote = All-monolithic storage ... (1024-bit NMOS) This new improvement of processor storage makes system expansion more economical. Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes.}}</ref> Megabyte was used to describe the 22-bit addressing of DEC ]/70 (1975)<ref name="PDP11">{{cite journal | last = Bell | first = Gordon | coauthors = Strecker, William | title = Computer structures: What have we learned from the PDP-11? | journal = ISCA '76: Proceedings of the 3rd annual symposium on Computer architecture | pages = pg 1–14 | publisher = ACM Press | date = November 1975 | url = http://research.microsoft.com/~gbell/Digital/Bell_Strecker_What_we%20_learned_fm_PDP-11c%207511.pdf
| quote = memory size (8k bytes to 4 megabytes).}}</ref> and gigabyte the 30-bit addressing DEC ]11/780 (1977).

By the mid 1970s it was common to see K (e.g Kbyte) meaning 1,024 and the occasional M (e.g. Mbyte) as 1,048,576 for words or bytes of computer memory (RAM) while K and M were commonly used with their decimal meaning for disk storage. In the 1980s the term G (e.g. GB) with decimal meaning was commonly applied to disk storage while M in its binary meaning became common for computer memory. In the 1990s G in its binary meaning became common usage for computer memory. The first TB hard disk drive (terabyte, decimal meaning) was introduced in 2007.<ref></ref>

The dual use of these prefixes as both decimal and binary quantities was defined in standards and dictionaries. The ] ANSI/IEEE Std 1084-1986<ref name="IEEE1084"> {{cite book | title= ANSI/IEEE Std 1084-1986 IEEE Standard Glossary of Mathematics of Computing Terminology |date=October 30, 1986 | url = http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=26589&isnumber=1030 |quote= kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 2<sup>10</sup>, or 1024. mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 2<sup>20</sup>, or 1,048,576.}}</ref> defined dual uses for kilo and mega. (The term "computer storage" means system memory.)<ref name="IBM360"/>
{{quote|
kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 2<sup>10</sup>, or 1024.

mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 2<sup>20</sup>, or 1,048,576.}} The binary units Kbyte and Mbyte were formally defined in ANSI/IEEE Std 1212-1991.<ref name = "IEEE1212">
{{cite book | title= ANSI/IEEE Std 1212-1991 IEEE Standard Control and Status Register (CSR) Architecture for Microcomputer Buses |date=July 22, 1992 | url = http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=4706&arnumber=182896&count=1|quote= Kbyte. Kilobyte. Indicates 2<sup>10</sup> bytes. Mbyte. Megabyte. Indicates 2<sup>20</sup>bytes. Gbyte is used in the Foreword.}}</ref> The terms Kbyte, Mbyte, and Gbyte are found in the trade press and in IEEE journals. "Gigabyte" was formally defined in IEEE Std 610.10-1994 as either 1,000,000,000 or 2<sup>30</sup> bytes.<ref name = "IEEE610">
{{cite book | title= IEEE Std 610.10-1994 IEEE Standard Glossary of Computer Hardware Terminology |date=June 24, 1994 | url = http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=477873&isnumber=10104 | quote= gigabyte (gig, GB). This term may mean either a) 1,000,000,000 bytes or b) 2<sup>30</sup> bytes. … As used in this document, the terms kilobyte (kB) means 2<sup>10</sup> or 1024 bytes, megabyte (MB) means 1024 kilobytes, and gigabyte (GB) means 1024 megabytes.}}</ref> Kilobyte, Kbyte, and KB are equivalent units and all are defined in the current standard, IEEE 100-2000.<ref name = "IEEE100">{{cite book | author = Institute of Electrical and Electronics Engineers| authorlink = Institute of Electrical and Electronics Engineers| title = The Authoritative Dictionary of IEEE Standards Terms | publisher = IEEE Computer Society Press | date = 2000 | url = http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4116787 | isbn = 0-7381-2601-2 }} "kB See kilobyte." "Kbyte Kilobyte. Indicates 2<sup>10</sup> bytes." "Kilobyte Either 1000 or 2<sup>10</sup> or 1024 bytes." The standard also defines megabyte and gigabyte. There is a note that an alternative notation for base-2 is under development. </ref>

The industry has coped with the dual definitions because system memory (RAM) typically uses the binary meaning while disk storage uses the decimal meaning. There are exceptions like ]s and ]s. There are no ] for computer storage capacity but the decimal prefix meanings of KB, MB, and GB are often referred to as SI prefixes.

While computer scientists typically used ''k'' to mean 1000, they recognized the convenience that would result from working with powers of 1024 and the confusion that resulted from using the same abbreviation for two definitions.<ref name="Morrison">''Letters to the editor: Abbreviations for computer and memory sizes''. Donald R. Morrison, ] Corp, Communications of the ACM, Volume 11, Issue 3 (March 1968) Page: 150 {{DOI|10.1145/362929.362962}}</ref> Several proposals for unique symbols were made in 1968. (At the time, memory size was small, and only ''K'' was in widespread use.) Donald Morrison proposed to use the Greek letter ] to denote 1024, κ² to denote 1024×1024, and so on.<ref name="Morrison"/> ] responded with a proposal to use bK as an abbreviation for 1024 and bK2 or bK² for 1024×1024, though he noted that neither the Greek letter nor lowercase letter b would be easy to reproduce on computer printers of the day.<ref>''Letters to the editor: proposed abbreviation for 1024: bK'', ], Applied National Lab, Communications of the ACM archive, Volume 11, Issue 6 (June 1968), Page: 391 {{DOI|10.1145/363347.363351}}</ref> ] further proposed that the units be abandoned altogether, and the letter B be used as a binary exponent, similar to ], to create shorthands like 3B20 for 3×2<sup>20</sup><ref>''Letters to the editor: On binary notation'', Bruce A. Martin, Associated Universities Inc., Communications of the ACM, Volume 11, Issue 10 (October 1968) Page: 658 {{DOI|10.1145/364096.364107}}</ref> None of these gained much acceptance, and capitalization of the letter K became the de facto standard for binary notation, though this could not be extended to higher powers. Later, as the discrepancy between the two systems increased, more proposals for unique units were made. ], who used decimal notation like 1 MB = 1000 kB,<ref name="Knuth">'''' Volume 1, ], pp. 24 and 94</ref> proposed that the powers of 1024 be designated as "large kilobytes" and "large megabytes" (abbreviated KKB and MMB).<ref name="Knuth"/> In 1996, ] proposed a system of units with di- prefixes, like the "dikilobyte" (K₂B or K2B).<ref>'''', ], ]</ref>

=== Consumer confusion ===

In the early days of computers there was little or no consumer confusion because of the sophisticated nature of the consumers and the practice of the computer manufacturers to specify (as opposed to ]) their products with decimal digits of sufficient places, e.g., the 1968 IBM stated System 360 "Model 91s can accommodate up to 6,291,496 bytes of main storage."<ref></ref>

Hard disk drive manufacturers used MB, i.e. 10<sup>6</sup> bytes, to characterize their products as early as 1974.<ref>The unambiguously uses MB to characterize HDD capacity in millions of bytes</ref> By 1977, in its first edition, Disk/Trend, a leading hard disk drive industry marketing consultancy segmented the industry according to MBs (decimal sense) of capacity.<ref>1977 Disk/Trend Report - Rigid Disk Drives, published June 1977</ref>


On the other hand, a hard disk whose capacity is specified by the manufacturer as "10 gigabytes" or "10&nbsp;GB", holds {{nowrap|10 × 10<sup>9</sup>}} = {{val|10000000000}} bytes, or a little more than that, but less than {{nowrap|10 × 2<sup>30</sup>}} = {{val|10737418240}} and a file whose size is listed as "2.3&nbsp;GB" may have a size closer to {{nowrap|2.3 × 2<sup>30</sup>}} ≈ {{val|2470000000}} or to {{nowrap|2.3 × 10<sup>9</sup>}} = {{val|2300000000}}, depending on the ] or ] providing that measurement. This kind of ambiguity is often confusing to computer system users and has resulted in ]s.<ref name="suitxxxx" /><ref name="sand2021" /> The IEC 60027-2 binary prefixes have been incorporated in the ] standard and are supported by other standards bodies, including the ], which defines the SI system,<ref name="BIPM8" />{{rp|p.121}} the ] ],<ref name="NIST1" /><ref name="NIST2" /> and the ].
The presentation of hard disk drive capacity by an operating system using MB in a binary sense appears no earlier than ] after 1984. Prior to that, on the systems that had a hard disk drive, capacity was presented in decimal digits with no prefix of any sort (e.g., MS/PC DOS ] command).


Prior to the 1999 IEC standard, some industry organizations, such as the ] (JEDEC), attempted to redefine{{citation needed|reason=We need sources that give specifics: it seems probable that no more than a mention of common use was made.|date=December 2024}} the terms ''kilobyte'', ''megabyte'', and ''gigabyte'', and the corresponding symbols ''KB'', ''MB'', and ''GB'' in the binary sense, for use in storage capacity measurements. However, other computer industry sectors (such as ]) continued using those same terms and symbols with the decimal meaning. Since then, the major standards organizations have expressly disapproved the use of SI prefixes to denote binary multiples, and recommended or mandated the use of the IEC prefixes for that purpose, but the use of SI prefixes in this sense has persisted in some fields.
See, for example, the following three images; consumers may be confused by the difference between the 160 GB on the disk drive package and the 149.05 GB reported by the operating system.


== Definitions ==
<gallery>
{{anchor|kibi|mebi|gibi|tebi|pebi|exbi|zebi|yobi|robi|quebi|IEC standard prefixes}}
Image:Seagate 160 GB hard drive box.jpg|This hard disk can hold 160×10<sup>9</sup> bytes, and is marketed using standard ]es as "160 GB"
Image:Windows XP Disk management for 160 GB disk.png|] lists the capacity of a 160×10<sup>9</sup> byte disk drive as "149.05 GB"
Image:Windows XP Drive Properties for 160 GB disk.png|Windows XP lists the capacity of a 160×10<sup>9</sup> byte disk drive as "152625 MB".
</gallery>


{| style="margin:auto;" class="wikitable"
== Prefixes ==
|+ Specific units of IEC 60027-2 A.2 and ISO/IEC 80000:13-2008
{|align="center" border="1" cellspacing="0" cellpadding="3" class="wikitable"
|- |-
!colspan="2"|IEC ! colspan="2"|IEC prefix
!colspan="5"| ! colspan="4"|Representations
!colspan="2"|Traditional
|- |-
! Name ! Name
! Symbol ! Symbol
! Base 2 ! Base 2
!colspan="2"| Base 16 ! Base 1024
! Value
!colspan="2"| Base 10
! Name ! Base 10
! Symbol
|- |-
| kibi | kibi
| Ki | Ki
| 2<sup>10</sup> | 2<sup>10</sup>
| 16<sup>2.5</sup> | 1024<sup>1</sup>
|align="right"| 400<sub>(16)</sub> | align="right"| {{val|1024}}
|align="right"| 1,024 | = {{val|1.024|e=3}}
|- style="background:#eee;"
| &gt; 10<sup>3</sup>
| ]
| k/K
|-bgcolor="#ffff99"
| mebi | mebi
| Mi | Mi
| 2<sup>20</sup> | 2<sup>20</sup>
| 16<sup>5</sup> | 1024<sup>2</sup>
|align="right"| 10&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1048576}}
| ≈ {{val|1.049|e=6}}
|align="right"| 1,048,576
| &gt; 10<sup>6</sup>
| ]
| M
|- |-
| gibi | gibi
| Gi | Gi
| 2<sup>30</sup> | 2<sup>30</sup>
| 16<sup>7.5</sup> | 1024<sup>3</sup>
|align="right"| 4000&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1073741824}}
| ≈ {{val|1.074|e=9}}
|align="right"| 1,073,741,824
|- style="background:#eee;"
| &gt; 10<sup>9</sup>
| ]
| G
|-bgcolor="#ffff99"
| tebi | tebi
| Ti | Ti
| 2<sup>40</sup> | 2<sup>40</sup>
| 16<sup>10</sup> | 1024<sup>4</sup>
|align="right"| 100&nbsp;0000&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1099511627776}}
| ≈ {{val|1.100|e=12}}
|align="right"| 1,099,511,627,776
| &gt; 10<sup>12</sup>
| ]
| T
|- |-
| pebi | pebi
| Pi | Pi
| 2<sup>50</sup> | 2<sup>50</sup>
| 16<sup>12.5</sup> | 1024<sup>5</sup>
|align="right"| 4&nbsp;0000&nbsp;0000&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1125899906842624}}
| ≈ {{val|1.126|e=15}}
|align="right"| 1,125,899,906,842,624
|- style="background:#eee;"
| &gt; 10<sup>15</sup>
| ]
| P
|-bgcolor="#ffff99"
| exbi | exbi
| Ei | Ei
| 2<sup>60</sup> | 2<sup>60</sup>
| 16<sup>15</sup> | 1024<sup>6</sup>
|align="right"| 1000&nbsp;0000&nbsp;0000&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1152921504606846976}}
| ≈ {{val|1.153|e=18}}
|align="right"| 1,152,921,504,606,846,976
| &gt; 10<sup>18</sup>
| ]
| E
|- |-
| zebi | zebi
| Zi | Zi
| 2<sup>70</sup> | 2<sup>70</sup>
| 16<sup>17.5</sup> | 1024<sup>7</sup>
|align="right"| 40&nbsp;0000&nbsp;0000&nbsp;0000&nbsp;0000<sub>(16)</sub> | align="right" | {{val|1180591620717411303424}}
| ≈ {{val|1.181|e=21}}
|align="right"| 1,180,591,620,717,411,303,424
|- style="background:#eee;"
| &gt; 10<sup>21</sup>
| ]
| Z
|-bgcolor="#ffff99"
| yobi | yobi
| Yi | Yi
| 2<sup>80</sup> | 2<sup>80</sup>
| 16<sup>20</sup> | 1024<sup>8</sup>
| align="right" | {{val|1208925819614629174706176}}
|align="right"| 1&nbsp;0000&nbsp;0000&nbsp;0000&nbsp;0000&nbsp;0000<sub>(16)</sub>
| ≈ {{val|1.209|e=24}}
|align="right"| 1,208,925,819,614,629,174,706,176
| &gt; 10<sup>24</sup>
| ]
| Y
|} |}


{{anchor|robi|quebi}}In 2022, the ] (BIPM) adopted the decimal prefixes ] for 1000<sup>9</sup> and ] for 1000<sup>10</sup>.<ref name="BIPM2022" /><ref name="gibn2022" /> In analogy to the existing binary prefixes, a consultation paper of the ]' Consultative Committee for Units (CCU) suggested the prefixes ''robi'' ({{nowrap|Ri, 1024<sup>9</sup>}}) and ''quebi'' ({{nowrap|Qi, 1024<sup>10</sup>}}) for their binary counterparts,<ref name="brown2023" /> but {{as of|2022|lc=yes}}, no corresponding binary prefixes have been adopted.<ref name="brown2022" />
=== Traditional binary prefixes ===


== Comparison of binary and decimal prefixes ==
Quantities that are multiples of the unit by a power of 2 are indicated using nearby SI prefixes, such as using kilo- (the SI prefix for 1000) to indicate 2<sup>10</sup>=1024. Byte multiples using binary powers up to yottabyte are given by the on-line computing dictionary ].<ref></ref>
The relative difference between the values in the binary and decimal interpretations increases, when using the SI prefixes as the base, from 2.4% for kilo to nearly 27% for the quetta prefix. Although the prefixes ronna and quetta have been defined, as of 2022 no names have been officially assigned to the corresponding binary prefixes.


{| class="wikitable" style="margin: auto;"
The one-letter symbols are identical to SI prefixes, except for "K", which is used interchangeably with "k" (in SI, ''only'' the lower-case "k" represents 1,000).
|- style="background:#ccf;"
! colspan="2" | Prefix
! colspan="2" | Binary ÷ Decimal
! colspan="2" | Decimal ÷ Binary
|- id="binary vs decimal kilo-"
| kilo || kibi
| 1.024 (+2.4%) || class="nowrap" |<div style="display:inline-block;width:102.4px;background:#000"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.9766 (−2.3%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:97.7px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal mega-"
| mega || mebi
| 1.049 (+4.9%) || class="nowrap" | <div style="display:inline-block;width:104.9px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.9537 (−4.6%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:95.4px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal giga-"
| giga || gibi
| 1.074 (+7.4%) || class="nowrap" | <div style="display:inline-block;width:107.4px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.9313 (−6.9%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:93.1px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal tera-"
| tera || tebi
| 1.100 (+10.0%) || class="nowrap" | <div style="display:inline-block;width:110.0px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.9095 (−9.1%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:90.9px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal peta-"
| peta || pebi
| 1.126 (+12.6%) || class="nowrap" | <div style="display:inline-block;width:112.6px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.8882 (−11.2%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:88.8px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal exa-"
| exa || exbi
| 1.153 (+15.3%) || class="nowrap" | <div style="display:inline-block;width:115.3px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.8674 (−13.3%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:86.7px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal zetta-"
| zetta || zebi
| 1.181 (+18.1%) || class="nowrap" | <div style="display:inline-block;width:118.1px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.8470 (−15.3%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:84.7px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal yotta-"
| yotta || yobi
| 1.209 (+20.9%) || class="nowrap" | <div style="display:inline-block;width:120.9px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.8272 (−17.3%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:82.7px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal yotta-"
| ronna || — <!-- editor note: please do not insert any binary prefix here (e.g. robi) until such a prefix is officially published, e.g. by the IEC -->
| 1.238 (+23.8%) || class="nowrap" | <div style="display:inline-block;width:123.8px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.8078 (−19.2%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:80.8px;background:#666;">&nbsp;</div></div>
|- id="binary vs decimal yotta-"
| quetta || — <!-- editor note: please do not insert any binary prefix here (e.g. quebi) until such a prefix is officially published, e.g. by the IEC -->
| 1.268 (+26.8%) || class="nowrap" | <div style="display:inline-block;width:126.8px;background:#000;"><div style="display:inline-block;width:100px;background:#666;">&nbsp;</div></div>
| 0.7889 (−21.1%) || class="nowrap" | <div style="display:inline-block;width:100px;background:#ccc;"><div style="display:inline-block;width:78.9px;background:#666;">&nbsp;</div></div>
|}


== History ==
These prefixes are in common use in contexts such as file and memory sizes. The names and values of the ] were defined in the 1960 SI standard, with powers-of-1000 values. Standard dictionaries do recognize the binary meanings for these prefixes.<ref name="webster">{{cite web|url=http://www.m-w.com/dictionary/Megabyte|title=Definition of megabyte|format=html}}</ref><ref name="metadict">{{cite web|url=http://dictionary.reference.com/browse/Megabyte|title=Definitions of Megabyte on Dictionnary.com"|format=html}}</ref> Oxford online dictionary defines, for example, megabyte as: "Computing a unit of information equal to one million or (strictly) 1,048,576 bytes."<ref name="oxford">{{cite web|url=http://www.askoxford.com/concise_oed/megabyte?view=uk|title=AskOxford: megabyte|format=html}}</ref>
{{See also|Timeline of binary prefixes}}


=== IEC standard prefixes === === Early prefixes ===
The original ] adopted by France in 1795 included two binary prefixes named '']-'' (2×) and '']-'' ({{sfrac|1|2}}×).<ref name="frev1795" /> However, these were not retained when the ]es were internationally adopted by the 11th ] in 1960.


=== Storage capacity ===
In January ], the ] introduced in an addendum to ] the prefixes ''kibi-'' (]), ''mebi-'', ''gibi-'', etc., and the symbols Ki, Mi, Gi, etc. to specify binary multiples of a quantity and eliminate the ambiguity with their ] meanings.<ref name="NIST-biprefix">{{cite web
==== Main memory ====
| url = http://physics.nist.gov/cuu/Units/binary.html
Early computers used one of two addressing methods to access the system memory; binary (base 2) or decimal (base 10).<ref name="weik1961" /> For example, the ] (1952) used a binary methods and could address 2048 ]s of 36 ]s each, while the ] (1953) used a decimal system, and could address ten thousand 7-bit words.
| title = "International System of Units (SI): Prefixes for binary multiples"
| work = The NIST Reference on Constants, Units, and Uncertainty
| publisher = ]
| accessdate = 2007-09-09
}}</ref>
The names for the new standard are derived from the original SI prefixes followed by "binary", such as "kilobinary", and can be shortened to a prefix like "kibi-". The new standard also clarifies that, from the point of view of the IEC, the SI prefixes will henceforth only have their base-10 meaning and never have a base-2 meaning.


By the mid-1960s, binary addressing had become the standard architecture in most computer designs, and main memory sizes were most commonly powers of two. This is the most natural configuration for memory, as all combinations of states of their ]s map to a valid address, allowing easy aggregation into a larger block of memory with contiguous addresses.
The second edition of the standard<ref>IEC 60027-2 (2000-11) Ed. 2.0</ref> defined them only up to ''exbi''-,<ref>{{cite journal|title=Prefixes for binary multiples|author=A.J.Thor|journal=Metrologica|date=2000|volume=37|issue=81|url=http://ej.iop.org/links/rDo33k,Nb/lrUHtuYE3BGiff6cav5vpA/me0112.pdf|format=PDF}}</ref> but in ], the third edition added prefixes ''zebi''- and ''yobi''-, thus matching all SI prefixes with their binary counterparts.<ref>{{cite press release|date=]|title=HERE COME ZEBI AND YOBI|publisher=International Electrotechnical Commission|url=http://www.iec.ch/news_centre/release/nr2005/nr2005.htm}}</ref>


While early documentation specified those memory sizes as exact numbers such as 4096, 8192, or {{val|16384}} units (usually ]s, bytes, or bits), computer professionals also started using the long-established metric system prefixes "kilo", "mega", "giga", etc., defined to be powers of 10,<ref name="BIPM8" /> to mean instead the nearest powers of two; namely, 2<sup>10</sup> = 1024, 2<sup>20</sup> = 1024<sup>2</sup>, 2<sup>30</sup> = 1024<sup>3</sup>, etc.<ref name="blais1930" /><ref name="liny1972" /> The corresponding metric prefix symbols ("k", "M", "G", etc.) were used with the same binary meanings.<ref name="real1959" /><ref name="gruen1960" /> The symbol for 2<sup>10</sup> = 1024 could be written either in lower case ("k")<ref name="horak2008" /><ref name="dodd1997" /><ref name="laver1989" /> or in uppercase ("K"). The latter was often used intentionally to indicate the binary rather than decimal meaning.<ref name="amda1964" /> This convention, which could not be extended to higher powers, was widely used in the documentation of the ] (1964)<ref name="amda1964" /> and of the ] (1972),<ref name="IBM1972" /> of the ],<ref name="CDC7600" /> of the DEC ]/70 (1975)<ref name="bell1975" /> and of the DEC ] (1977).{{citation needed|date=August 2023}}
On ], ] the IEEE standard ] (Prefixes for Binary Multiples) was elevated to a full-use standard by the IEEE Standards Association after a two-year trial period.<ref>{{cite web |url=http://standards.ieee.org/board/rev/305agenda.html |title=IEEE-SA STANDARDS BOARD STANDARDS REVIEW COMMITTEE (RevCom) MEETING AGENDA |accessdate=2007-02-25 |date=] |quote='''1541-2002''' (SCC14) IEEE Trial-Use Standard for Prefixes for Binary Multiples '''' <u>Recommendation</u>: Elevate status of standard from trial-use to full-use. Editorial staff will be notified to implement the necessary changes. The standard will be due for a maintenance action in 2007.}}</ref>


In other documents, however, the metric prefixes and their symbols were used to denote powers of 10, but usually with the understanding that the values given were approximate, often truncated down. Thus, for example, a 1967 document by ] (CDC) abbreviated "2<sup>16</sup> = {{nowrap|64 × 1024}} = {{val|65536}} words" as "65K words" (rather than "64K" or "66K"),<ref name="CDC1967" /> while the documentation of the ] real-time computer (1974) denoted {{nowrap|3 × 2<sup>16</sup>}} = {{nowrap|192 × 1024}} = {{val|196608}} as "196K" and 2<sup>20</sup> = {{val|1048576}} as "1M".<ref name="frank1974" />
The harmonized ]/] ] standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005 (those defining Prefixes for binary multiples).


These three possible meanings of "k" and "K" ("1024", "1000", or "approximately 1000") were used loosely around the same time, sometimes by the same company. The ] business computer (1973) could have "64K", "96K", or "128K" bytes of memory.<ref name="HP1973" /> The use of SI prefixes, and the use of "K" instead of "k" remained popular in computer-related publications well into the 21st century, although the ambiguity persisted. The correct meaning was often clear from the context; for instance, in a binary-addressed computer, the true memory size had to be either a power of 2, or a small integer multiple thereof. Thus a "512 megabyte" RAM module was generally understood to have {{nowrap|512 × 1024<sup>2</sup>}} = {{val|536870912}} bytes, rather than {{val|512000000}}.
] (the International Bureau of Weights and Measures which maintains ]) expressly prohibits the binary prefix usage, and recommends the use of ] as an alternative since computing units are not included in SI.<ref name="BIPM">
{{cite book |title=The International System of Units (SI) |url=http://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf |format=PDF |accessdate=2007-02-25 |edition=8th edition |year=2006 |publisher=STEDI Media |location=Paris |language=French/English |isbn=92-822-2213-6 |pages=p. 127 |chapter=§3.1 SI prefixes |quote= These SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The IEC has adopted prefixes for binary powers in the international standard IEC 60027-2: 2005, third edition, ''Letter symbols to be used in electrical technology — Part 2: Telecommunications and electronics''. The names and symbols for the prefixes corresponding to 2<sup>10</sup>, 2<sup>20</sup>, 2<sup>30</sup>, 2<sup>40</sup>, 2<sup>50</sup>, and 2<sup>60</sup> are, respectively: kibi, Ki; mebi, Mi; gibi, Gi; tebi, Ti; pebi, Pi; and exbi, Ei. Thus, for example, one kibibyte would be written: 1 KiB = 2<sup>10</sup> B = 1024 B, where B denotes a byte. Although these prefixes are not part of the SI, they should be used in the field of information technology to avoid the incorrect usage of the SI prefixes.}}
</ref>. The binary definition of the prefixes k, M, G etc is not permitted by the United States ] (NIST).<ref name=sp330>{{cite book |author=Barry N. Taylor & Ambler Thompson Ed. |title= The International System of Units (SI)|origyear= 2008 |url=http://physics.nist.gov/Pubs/SP330/sp330.pdf |accessdate=2008-6-18|publisher=National Institute of Standards and Technology|location= Gaithersburg, MD|pages=23}} </ref>


==== Hard disks ====
=== Approximate ratios between binary and decimal prefixes ===
In specifying disk drive capacities, manufacturers have always used conventional decimal SI prefixes representing powers of 10. Storage in a rotating ] is organized in platters and tracks whose sizes and counts are determined by mechanical engineering constraints so that the capacity of a disk drive has hardly ever been a simple multiple of a power of 2. For example, the first commercially sold disk drive, the ] (1956), had 50 physical disk platters containing a total of {{val|50000}} sectors of 100 characters each, for a total quoted capacity of 5 million characters.<ref name="IBM1956" />


Moreover, since the 1960s, many disk drives used IBM's ], where each track was divided into blocks of user-specified size; and the block sizes were recorded on the disk, subtracting from the usable capacity. For example, the IBM 3336 disk pack was quoted to have a 200-megabyte capacity, achieved only with a single {{val|13030}}-byte block in each of its 808 × 19 tracks.
As the order of magnitude increases, the percentage difference between the binary and decimal values of a prefix increases, from 2.4% (with the kilo prefix) to over 20% (with the ''yotta'' prefix). This makes differentiating between the two increasingly important as larger and larger data storage and transmission technologies are developed.


Decimal megabytes were used for disk capacity by the CDC in 1974.<ref name="CDC1974" /> The Seagate ],<ref name="seag1982" /> one of several types installed in the ],<ref name="CSN1984" /> had a capacity of {{val|10027008|u=bytes}} when formatted as 306 × 4 tracks and 32 256-byte sectors per track, which was quoted as "10&nbsp;MB".<ref name="mall2011" /> Similarly, a "300&nbsp;GB" hard drive can be expected to offer only slightly more than {{val|300|e=9}} = {{val|300000000000}}, bytes, not {{nowrap|300 × 2<sup>30</sup>}} (which would be about {{val|322|e=9}} bytes or "322&nbsp;GB"). The first terabyte (SI prefix, {{val|1000000000000}} bytes) hard disk drive was introduced in 2007.<ref name="hita2007" /> Decimal prefixes were generally used by information processing publications when comparing hard disk capacities.<ref name="RDD1977" />
{|align="center" border="1" cellspacing="0" cellpadding="3" class="wikitable"
|-bgcolor="#ccccff"
! Name
! Bin ÷ Dec
! Dec ÷ Bin
! Percentage difference
|-
| ]&nbsp;: ]
| 1.024
| 0.976
| +2.4% or −2.3%
|-bgcolor="#ffff99"
| ]&nbsp;: ]
| 1.049
| 0.954
| +4.9% or −4.6%
|-
| ]&nbsp;: ]
| 1.074
| 0.931
| +7.4% or −6.9%
|-bgcolor="#ffff99"
| ]&nbsp;: ]
| 1.100
| 0.909
| +10.0% or −9.1%
|-
| ]&nbsp;: ]
| 1.126
| 0.888
| +12.6% or −11.2%
|-bgcolor="#ffff99"
| ]&nbsp;: ]
| 1.153
| 0.867
| +15.3% or −13.3%
|-
| ]&nbsp;: ]
| 1.181
| 0.847
| +18.1% or −15.3%
|-bgcolor="#ffff99"
| ]&nbsp;: ]
| 1.209
| 0.827
| +20.9% or −17.3%
|}


Some programs and operating systems, such as ], still use "MB" and "GB" to denote binary prefixes even when displaying disk drive capacities and file sizes, as did ]. Thus, for example, the capacity of a "10 MB" (decimal "M") disk drive could be reported as "{{nowrap|9.56 MB}}", and that of a "300&nbsp;GB" drive as "279.4&nbsp;GB". Some operating systems, such as ],<ref>{{cite web |title=How iOS and macOS report storage capacity |url=https://support.apple.com/en-us/HT201402 |website=Apple Support |access-date=9 January 2022 |language=en |date=27 February 2018 |archive-date=9 April 2020 |archive-url=https://web.archive.org/web/20200409170256/https://support.apple.com/en-us/HT201402 |url-status=live }}</ref> ],<ref>{{cite web |title=UnitsPolicy |url=https://wiki.ubuntu.com/UnitsPolicy |website=Ubuntu Wiki |publisher=Ubuntu |access-date=9 January 2022 |archive-date=18 November 2021 |archive-url=https://web.archive.org/web/20211118114902/https://wiki.ubuntu.com/UnitsPolicy |url-status=live }}</ref> and ],<ref>{{cite web |title=ConsistentUnitPrefixes |url=https://wiki.debian.org/ConsistentUnitPrefixes |website=Debian Wiki |access-date=9 January 2022 |archive-date=3 December 2021 |archive-url=https://web.archive.org/web/20211203075715/https://wiki.debian.org/ConsistentUnitPrefixes |url-status=live }}</ref> have been updated to use "MB" and "GB" to denote decimal prefixes when displaying disk drive capacities and file sizes. Some manufacturers, such as ], have released recommendations stating that properly-written software and documentation should specify clearly whether prefixes such as "K", "M", or "G" mean binary or decimal multipliers.<ref name="seaga2011" /><ref name="seag2010" />
''Example:'' 300&nbsp;GB ≅ 279.5&nbsp;GiB.


== Usage notes == ==== Floppy disks ====
] used ], and their capacities was usually specified with SI-like prefixes "K" and "M" with either decimal or binary meaning. The capacity of the disks was often specified without accounting for the internal ] overhead, leading to more irregularities.


The early 8-inch diskette formats could contain less than a megabyte with the capacities of those devices specified in kilobytes, kilobits or megabits.<ref>{{Cite web |date=2012-03-07 |title=IBM100 – The Floppy Disk |url=http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/floppy/breakthroughs/ |archive-url=https://web.archive.org/web/20120403025215/http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/floppy/breakthroughs/ |url-status=dead |archive-date=3 April 2012 |access-date=2023-10-17 |website=www-03.ibm.com |language=en-US}}</ref><ref>{{cite magazine|magazine=Datamation |title=Disc Storage |date= May 1972 |pages=154, 162, 164 |quote= CDS 100 ... stores over 600 kilobits, Model 650 ... store 1.5 megabits ... }}</ref>
In this section, the phrase "decimal unit" is used to denote "SI designation understood in its standard, decimal, power-of-1000 sense" and "binary unit" means "SI designation understood in its binary, power-of-1024 sense." The symbol '''B''' means byte as per computer-industry standard (] and ]).


The 5.25-inch diskette sold with the ] could hold {{nowrap|1200 × 1024}} = {{val|1228800}} bytes, and thus was marketed as "1200&nbsp;KB" with the binary sense of "KB".<ref>{{Cite web |last=Brutman |first=Michael B. |date=July 8, 2001 |title=Working with Disks: An intro to floppy disks and floppy drives |url=http://brutmanlabs.org/Diskettes/Diskette_handling.html |website=Brutmanlabs |access-date=2024-02-19 |archive-date=2024-02-19 |archive-url=https://web.archive.org/web/20240219085221/http://brutmanlabs.org/Diskettes/Diskette_handling.html |url-status=dead }}</ref> However, the capacity was also quoted "1.2&nbsp;MB",<ref>{{Cite web |title=Floppy disk storage {{!}} IBM |url=https://www.ibm.com/history/floppy-disk#1970s+high-density+storage |access-date=2024-12-14 |website=www.ibm.com |language=en}}</ref> which was a hybrid decimal and binary notation, since the "M" meant 1000 × 1024. The precise value was {{val|1.2288|u=MB}} (decimal) or {{val|1.171875|u=MiB}} (binary).
Certain units are always understood as decimal even in computing contexts. For example, ] (Hz), which is used to measure ''']s''' of electronic components, and bit/s, used to measure ''']'''. So a 1 GHz processor performs 1,000,000,000 clock ticks per second, a 128 kbit/s<!--- Truly kbit for kilobit, no Kbit please ---> ] stream consumes 128,000 bits (16 kB, 15.625 KiB) per second, and a 1&nbsp;Mbit/s Internet connection can transfer 1,000,000 bits (125 kB, approx 122 KiB) per second, assuming an 8-bit byte, and no overhead.<ref></ref>


The 5.25-inch ] had 256 bytes per sector, 13 sectors per track, 35 tracks per side, or a total capacity of {{val|116480}} bytes. It was later upgraded to 16 sectors per track, giving a total of {{nowrap|140 × 2<sup>10</sup>}} = {{val|143360}} bytes, which was described as "140KB" using the binary sense of "K".
=== Pronunciation ===


The most recent version of the physical hardware, the "3.5-inch diskette" cartridge, had 720 512-byte blocks (single-sided). Since two blocks comprised 1024 bytes, the capacity was quoted "360&nbsp;KB", with the binary sense of "K". On the other hand, the quoted capacity of "1.44&nbsp;MB" of the High Density ("HD") version was again a hybrid decimal and binary notation, since it meant 1440 pairs of 512-byte sectors, or {{nowrap|1440 × 2<sup>10</sup>}} = {{val|1474560|u=bytes}}. Some operating systems displayed the capacity of those disks using the binary sense of "MB", as "1.4&nbsp;MB" (which would be {{nowrap|1.4 × 2<sup>20</sup>}} ≈ {{val|1468000|u=bytes}}). User complaints forced both Apple{{citation needed|date=August 2023}} and Microsoft<ref name="msoftxxxx" /> to issue support bulletins explaining the discrepancy.
It is suggested that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced as "bee."<ref name="NIST"/>


=== Files === ==== Optical disks ====
When specifying the capacities of optical ]s, "megabyte" and "MB" usually meant 1024<sup>2</sup>&nbsp;bytes. Thus a "700-MB" (or "80-minute") CD has a nominal capacity of about {{val|700|u=MiB}}, which is approximately {{val|730|u=MB}} (decimal).<ref name="cdromcap" />


On the other hand, capacities of other ] storage media like ], ], ] and ] have been generally specified in decimal gigabytes ("GB"), that is, 1000<sup>3</sup> bytes. In particular, a typical "{{val|4.7|u=GB}}" DVD has a nominal capacity of about {{val|4.7|e=9|u=bytes}}, which is about {{val|4.38|u=GiB}}.<ref name="dvdcap" />
Prior to the ] ] (i.e., 1984) file sizes were typically reported by the operating system in decimal digits without prefixes of any sort (e.g. ], ], IBM ]{{Clarifyme}}<!-- Is this supposed to be IBM MVS or DEC VMS? -->, ], ], etc.). Today most operating systems report file size with powers of 1024 indicated as KB/MB/... (with or without the B); however, some systems also report decimal digits (e.g. ]) and some give provide flags to allow binary or decimal prefixes (e.g. some ]es).


==== Tape drives and media ====
Some verified examples in alphabetical order:
Tape drive and media manufacturers have generally used SI decimal prefixes to specify the maximum capacity,<ref name="IBMt2016" /><ref name="ECMA2013" /> although the actual capacity would depend on the ] used when recording.


==== Data and clock rates ====
* ] ]{{Fact|date=March 2008}} <!-- informed guess because of its Unix ancestry and comments elsewhere, explicit version and similar verification required because unavailable to the author at this time -->
Computer ] frequencies are always quoted using SI prefixes in their decimal sense. For example, the internal clock frequency of the original ] was {{val|4.77|u=MHz}}, that is {{val|4770000|u=Hz}}.
* ] uses 1024 for command line and file manager. The ] ] reports a 2021-byte file as 2021 with "ls -l" (to get the exact number of bytes), 2.0K with "ls -lh" (with powers of 1024 by default), or as 2.1k with "ls -lh --si" (with --si to explicitly ask for powers of 1000, note the lower-case k), evidently rounding up all values according to the number of decimals reported. The file manager on the verified versions (]) reports this same file as having size "2.0 KB".<ref>{{cite web | url = http://www.perpetualpc.net/srtd_ls.html | title = command reference}}</ref>
* ] 2000 version 5.00.2195 Service Pack 2 and XP version 2002 Service Pack 2 as displayed in Windows Explorer and elsewhere.
* ] ] uses 1024 for command line and file manager.<ref></ref><ref>Verified on the downloadable versions for Solaris on 24 February 2008: Solaris 10 8/07 and Solaris Express Developer Edition 1/08</ref> The ls command reports a 2021-byte file as 2021 with "ls -l" (to get the exact number of bytes), 2.0K with "ls -lh" (with only powers of 1024 available), evidently rounding up all values according to the number of decimals reported. The file manager on the ] on the verified versions (GNOME Nautilus) reports this same file as having size "2.0 KB".


Similarly, digital information transfer rates are quoted using decimal prefixe. The ] "{{val|100|u=MB/s}}" disk interface can transfer {{val|100000000}} bytes per second, and a "{{val|56|u=Kb/s}}" modem transmits {{val|56000}} bits per second. Seagate specified the sustained transfer rate of some hard disk drive models with both decimal and IEC binary prefixes.<ref name="seaga2011" />
=== Hardware ===
The standard sampling rate of music ]s, quoted as {{val|44.1|u=kHz}}, is indeed {{val|44100}} samples per second.{{citation needed|date=August 2023}} A "{{val|1|u=Gb/s}}" ] interface can receive or transmit up to 10<sup>9</sup> bits per second, or {{val|125000000}} bytes per second within each packet. A "]" modem can encode or decode up to {{val|56000}} bits per second.
==== Computer memory ====


Decimal SI prefixes are also generally used for ] speeds. A ] bus with {{val|66|u=MHz}} clock and 64 bits wide can transfer {{val|66000000}} 64-bit words per second, or {{val|4224000000|u=bit/s}} = {{val|528000000|u=B/s}}, which is usually quoted as {{val|528|u=MB/s}}. A ] memory on a ] bus, transferring 8 bytes per cycle with a clock speed of {{val|200|u=MHz}} has a bandwidth of {{nowrap|{{val|200000000}} × 8 × 2}} = {{val|3200000000|u=B/s}}, which would be quoted as {{val|3.2|u=GB/s}}.
]


=== Ambiguous standards ===
Measurements of most types of electronic ''']''' such as ] and ] and ] (large scale disk-like flash is sometimes an exception) are given in binary units, as they are made in power-of-two sizes. This is the most natural configuration for memory, as all combinations of their address lines map to a valid address, allowing easy aggregation into a larger contiguous block of memory.
The ambiguous usage of the prefixes "kilo ("K" or "k"), "mega" ("M"), and "giga" ("G"), as meaning both powers of 1000 or (in computer contexts) of 1024, has been recorded in popular dictionaries,<ref name="webster" /><ref name="metadict" /><ref name="oxford" /> and even in some obsolete standards, such as ]<ref name="ansi1986" /> and ],<ref name="ieee1992" /> ],<ref name="ieee1994" /> and ].<ref name="ieee2000" /> Some of these standards specifically limited the binary meaning to multiples of "byte" ("B") or "bit" ("b").


=== Early binary prefix proposals ===
JEDEC Solid State Technology Association, the semiconductor engineering standardization body of the Electronic Industries Alliance (EIA) in Standard 100B.01<ref name="JEDEC">{{Citation | last = JEDEC Solid State Technology Association
Before the IEC standard, several alternative proposals existed for unique binary prefixes, starting in the late 1960s. In 1996, ] proposed the extra prefix "di" and the symbol ] or ] "2" to mean "binary"; so that, for example, "one dikilobyte" would mean "1024 bytes", denoted "K<sub>2</sub>B" or "K2B".<ref name="kuhn1996" />
| title = Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits | url = http://www.jedec.org/download/search/JESD100B01.pdf | journal = JESD 100B.01 |date=December 2002}}</ref> continues to include definitions in the binary sense K, M and G as prefixes to units of semiconductor memory (see ]), noting that these definitions are “only included to reflect common usage” and noting that ‘IEEE/ASTM SI 10-1997 states “This practice frequently leads to confusion and is deprecated.”’. All standards published by JEDEC use the common usage, including end-user packaging recommendations for memory chips.


In 1968, Donald Morrison proposed to use the Greek letter kappa (]) to denote 1024, κ<sup>2</sup> to denote 1024<sup>2</sup>, and so on.<ref name="morr1968" /> (At the time, memory size was small, and only K was in widespread use.) In the same year, ] responded with a suggestion to use bK as an abbreviation for 1024 and bK2 or bK<sup>2</sup> for 1024<sup>2</sup>, though he noted that neither the Greek letter nor lowercase letter b would be easy to reproduce on computer printers of the day.<ref name="give1968" /> ] of ] proposed that, instead of prefixes, binary powers of two were indicated by the letter ] followed by the exponent, similar to ] in ]. Thus one would write 3B20 for {{nowrap|3 × 2<sup>20</sup>}}.<ref name="mart1968" /> This convention is still used on some calculators to present binary floating point-numbers today.<ref name="schw1993" />
Many computer programming tasks naturally reference memory in terms of ]. For example, a 16-bit ] can reference at most 65,536 items (bytes, words, or other objects), or an operating system might map memory in terms of 4,096-byte pages, in which case exactly 8,192 pages could be allocated within 33,554,432 bytes of hardware memory. It is convenient to informally express these numbers, respectively, as 64K items, or as 8K pages of 4 Kbytes (KiB) each within 32 MBytes (MiB) of memory. A programmer can easily mentally calculate that "8K &times; 4K is 32 meg" and get it exactly right, within this powers-of-two context. This convenience is likely one source of originally adapting "kilo" and "mega" from SI as shorthand for 1,024 and 1,048,576, as specialized jargon within a segment of the industry.


In 1969, ], who uses decimal notation like 1&nbsp;MB = 1000&nbsp;kB,<ref name="knuth2016" /> proposed that the powers of 1024 be designated as "large kilobytes" and "large megabytes", with abbreviations KKB and MMB.<ref name="knuth1999" />
Almost all computer user tasks (and many high-level programming tasks) have no natural affinity or need for explicit powers of two. The consumer confusion between powers of 1000 and powers of 1024 may derive largely from some operating systems and applications that were originally written by and for programmers, and which thus reported quantities such as file sizes in familiar (to programmers) powers of 1024 while using SI (powers of 1000) abbreviations. Without such reporting, most users might not have been substantially exposed to powers of 1024, as the net memory available to users after various overheads is rarely a power of two. This legacy behavior of operating systems reporting sizes in powers of 1024 has continued to this day (in 2008) even in many GUI oriented operating systems intended mainly for non-programmers.


==== Hard disk drives ==== === Consumer confusion ===
The ambiguous meanings of "kilo", "mega", "giga", etc., has caused significant ], especially in the ] era. A common source of confusion was the discrepancy between the capacities of hard drives specified by manufacturers, using those prefixes in the decimal sense, and the numbers reported by operating systems and other software, that used them in the binary sense, such as the ] in 1984. For example, a hard drive marketed as "1&nbsp;TB" could be reported as having only "931&nbsp;GB". The confusion was compounded by fact that RAM manufacturers used the binary sense too.


=== Legal disputes ===
] manufacturers mostly state capacity in decimal units. This usage has a long tradition, even predating the ] adopted in 1960, as follows:
The different interpretations of disk size prefixes led to class action lawsuits against digital storage manufacturers. These cases involved both flash memory and hard disk drives.
* The first disk drive the ] (1950s) had 5 million 6 bit characters organized in 100 character sectors (i.e., blocks). This predates the SI system.
* In the 1960s most disk drives used IBM's variable block length format (called, ] or "CKD").<ref>IBM invented the disk drive in 1956 and until the late 1960s its drives and their clones were dominant. See, e.g. , especially IBM analyses of Memorex and other disk drive companies.</ref> Any block size could be specified up to the maximum track length. Blocks ("records" in IBM's terminology) of 88, 96, 880 and 960 were often used because they related to the fixed block size of punch cards. The drive capacity was usually stated in full track record blocking, for example, the 100 megabyte 3336 disk pack only achieved that capacity with a full track block size of 13,030 bytes.
* CKD continued into the 1990s and perhaps into this day. In the 1970s and 1980s most drives were specified with unformatted tracks (the unformatted capacity) with the particular block size and formatted capacity a function of the controller design. For example, the ST412 of IBM PC/XT fame had an unformatted capacity of 12.75 MB (12.75×10<sup>6</sup> ]) and with the Xebec controller and 512 byte blocks it formatted to and was advertised as a 10.0 MB (10.0×10<sup>6</sup> B) HDD. Other controllers supported other block sizes resulting in other formatted capacities.
* The advent of intelligent interfaces (] and ]) in the early 1990s took the block size decision into the drive and virtually all chose 512 bytes, for no reason other than that was what IBM had chosen when they picked the Xebec controller for the PC/XT. Capacity continued to be specified by the HDD manufacturers with SI prefix definitions.
], most, if not all, HDD manufacturers continue to use decimal prefixes to identify capacity.<ref>
On ] ], a check of the websites of Fujitsu, HGST, Samsung, Seagate, Toshiba and Western Digital showed these companies (representing virtually all of the HDD industry by unit volume) specify capacity with the SI prefix definitions.
</ref>


==== Flash drives ==== ==== Early cases ====
Early cases (2004–2007) were settled prior to any court ruling with the manufacturers admitting no wrongdoing but agreeing to clarify the storage capacity of their products on the consumer packaging. Accordingly, many flash memory and hard disk manufacturers have disclosures on their packaging and web sites clarifying the formatted capacity of the devices or defining MB as 1&nbsp;million bytes and 1&nbsp;GB as 1&nbsp;billion bytes.<ref name="wdc2007" /><ref name="flash2016" /><ref name="sand2013" /><ref name="sd-cap-disclaimer" />


==== ''Willem Vroegh v. Eastman Kodak Company'' ====
] and Flash-based memory cards like ] and ] are typically classified in "powers of two" multiples of decimal megabytes; for example, a "256 MB" card would hold 256 million bytes.<ref name="sd-cap-disclaimer">{{cite web
On 20 February 2004, ] against Lexar Media, Dane–Elec Memory, ], ] Company, Kingston Technology Company, Inc., ] Products, Inc.; ] Inc., ], ], and ] alleging that their descriptions of the capacity of their ] cards were false and misleading.
| url = http://www.sandisk.com/Assets/Categories/Products/sd_capacitydisclaimer.pdf
| title = "Secure Digital Capacity Disclaimer"
| format = ]
| work = sandisk.com
| publisher = ]
| accessdate = 2007-09-09
}}</ref>
Although the devices usually have at least the expected byte capacity, each manufacturer allocates different portions of the device's ultimate capacity for such things as ].


Vroegh claimed that a 256&nbsp;MB Flash Memory Device had only 244&nbsp;MB of accessible memory. "Plaintiffs allege that Defendants marketed the memory capacity of their products by assuming that one megabyte equals one million bytes and one gigabyte equals one billion bytes." The plaintiffs wanted the defendants to use the customary values of 1024<sup>2</sup> for megabyte and 1024<sup>3</sup> for gigabyte. The plaintiffs acknowledged that the IEC and IEEE standards define a MB as one million bytes but stated that the industry has largely ignored the IEC standards.<ref name="vreo2005" />
==== Floppy drives ====


The parties agreed that manufacturers could continue to use the decimal definition so long as the definition was added to the packaging and web sites.<ref name="sand2012" /> The consumers could apply for "a discount of ten percent off a future online purchase from Defendants' Online Stores Flash Memory Device".<ref name="safi2007" />
Floppy disk drive and media manufacturers use decimal units for unformatted recording capacity while most computer operating systems use binary units to measure the formatted capacity. The original ] (1981) used a ] 5¼ inch floppy disk drive. The single sided drive was rated at 250 kilobytes (unformatted) and the double sided version was rated at 500 kilobytes.<ref>{{cite book | last =Tandon | authorlink = | title =TM100-1, TM100-2 Flexible Disk Drives: Product Specification and User's Manual | publisher =Tandon Corporation | date = Janurary1984 | pages = pg 2-4 | url = http://www.bitsavers.org/pdf/tandon/TM100-1_userMan_1984.pdf}}</ref>


==== ''Orin Safier v. Western Digital Corporation'' ====
A 5¼ inch diskette recorded at double density ] will hold 6,250 bytes per track and has 40 tracks per side, yielding 250,000 bytes per side. To make it practical to record smaller blocks of data, the tracks are formatted into sectors with gaps between them. The gaps allow individual sectors to be recorded without overwriting adjacent sectors. Each sector also has additional header bytes to identify the sector.
On 7 July 2005, an action entitled ''Orin Safier v. ] Corporation, et al.'' was filed in the Superior Court for the City and County of San Francisco, Case No. CGC-05-442812. The case was subsequently moved to the Northern District of California, Case No. 05-03353 BZ.<ref name="gutr2006" />


Although Western Digital maintained that their usage of units is consistent with "the indisputably correct industry standard for measuring and describing storage capacity", and that they "cannot be expected to reform the software industry", they agreed to settle in March 2006 with 14 June 2006 as the Final Approval hearing date.<ref name="zimm2006" />
With ] 1.0 and 1.1, each track has 8 sectors of 512 bytes and this provides 163,840 bytes per side (8&nbsp;× 512&nbsp;× 40). The IBM user documentation referred to this as "160KB" for single sided diskette and "320KB" for double sided diskette.<ref name="DOS 1.1">{{cite book | last =IBM | title =Disk Operating System by Microsoft (Version 1.1) | publisher =IBM Corporation | date = May 1982 | location = | pages = G-1}} Some software applications "used with DOS 1.10, will operate with either two 160KB drives or two 320KB drives. Both drives MUST be of the same type…" </ref> Starting with PC-DOS 2.0 (1983), each track had 9 sectors of 512 bytes. The formatted capacity was increased to 184,320 bytes per side or 368,640 bytes per diskette. The IBM documentation referred to these as "180KB" and "360KB" diskettes. The same drives and media can have different capacities depending on format.<ref name = "DOS 2.0">{{cite book | last =IBM | title =Disk Operating System by Microsoft (Version 2.0) | publisher =IBM Corporation | date = January 1983 | location = | pages = A-2}} "Beginning with DOS Version 2.00, DOS formats diskettes at 9 sectors per track, which increases capacity from 163,840 to 184,320 characters of information for single-sided diskettes and from 327,680 to 368,640 characters for dual-sided diskettes. The smaller capacity diskettes created by DOS Version 1.00 or DOS Version 1.10 (8 sectors per track) are also usable with DOS Version 2.00." </ref>


Western Digital offered to compensate customers with a ] download of backup and recovery software that they valued at US$30. They also paid {{val|p=$|500000}} in fees and expenses to San Francisco lawyers Adam Gutride and Seth Safier, who filed the suit. The settlement called for Western Digital to add a disclaimer to their later packaging and advertising.<ref name="betaxxxx" /><ref name="reim2006" /><ref name="wdc2010" />
On all diskettes the capacity available to the user will be smaller that the total number of sectors because some are reserved by the operating system for ] or directory tables.
<!--- I think that to end on this bit is overly POV. I'll leave it to someone else to add. – jeh--->
Western Digital had this footnote in their settlement. "Apparently, Plaintiff believes that he could sue an egg company for fraud for labeling a carton of 12 eggs a 'dozen', because some bakers would view a 'dozen' as including 13 items."<ref name="bask2006" />


==== ''Cho v. Seagate Technology (US) Holdings, Inc.'' ====
The ] (1984) had a new 5¼ inch disk drive that had 80 tracks per side, rotated at 360 rpm (versus 300 rpm) and had a new diskette media. The formatted capacity was 1,228,800 bytes or 1200&nbsp;KB. (80 tracks&nbsp;× 15 sectors&nbsp;× 512 bytes&nbsp;× 2 sides)
A lawsuit (''Cho v. Seagate Technology (US) Holdings, Inc.'', San Francisco Superior Court, Case No. CGC-06-453195) was filed against ], alleging that Seagate overrepresented the amount of usable storage by 7% on hard drives sold between 22 March 2001 and 26 September 2007. The case was settled without Seagate admitting wrongdoing, but agreeing to supply those purchasers with gratis backup software or a 5% refund on the cost of the drives.<ref name="seagb2011" />


==== ''Dinan et al. v. SanDisk LLC'' ====
The ] (1986) used the 3½ inch diskettes. These were similar in recording technology to the original 5¼ inch drives except they had 80 tracks per side. The formatted capacity was 737,280 bytes or 720&nbsp;KB. Apple used the same disk with a different recording technology, ], that gave a formatted capacity of 819,200 bytes or 800&nbsp;KB. Apple referred to this as an "800K" disk.<ref name="Apple 800K">{{cite web | last =Apple Inc. | title = Double-Density Versus High-Density Disks | publisher = Apple Inc. | date =1991-08-22 | url = http://docs.info.apple.com/article.html?artnum=3802| work = Article ID: 3802
On 22 January 2020, the district court of the Northern District of California ruled in favor of the defendant, SanDisk, upholding its use of "GB" to mean {{val|1000000000|u=bytes}}.<ref name="suitbxxxx" />
| accessdate = 2007-07-07}} "This article gives the specifications for the 800K floppy disks and the 1.4MB floppy disks." 800K Disk has 1600 sectors and 1.4MB Disk has 2880 sectors. A sector is 512 bytes. </ref>


=== IEC 1999 Standard ===
The last widely adopted diskette was the 3½ inch high density. This has twice the capacity as the 720&nbsp;KB diskettes, 1,474,560 bytes or 1440&nbsp;KB. The drive was marketed as 1.44&nbsp;MB when a more accurate value would have been 1.4&nbsp;MB (1.40625&nbsp;MB). Some users have noticed the missing 0.04&nbsp;MB and both Apple and Microsoft have support bulletins referring to them as 1.4 MB.<ref name="Microsoft 121839"> {{cite web | last =Microsoft | title = Determining Actual Disk Size: Why 1.44 MB Should Be 1.40 MB | work = Article ID: 121839 | publisher =Microsoft | date = 2003-05-06 | url = http://support.microsoft.com/kb/121839 | accessdate = 2007-07-07}} "The 1.44-megabyte (MB) value associated with the 3.5-inch disk format does not represent the actual size or free space of these disks. Although its size has been popularly called 1.44 MB, the correct size is actually 1.40 MB." </ref><ref name="Apple 800K"/> The 1200&nbsp;KB 5¼ inch diskette was marketed as 1.2&nbsp;MB (1.171875&nbsp;MiB) without any controversy.
In 1995, the ]'s (IUPAC) Interdivisional Committee on Nomenclature and Symbols (IDCNS) proposed the prefixes "kibi" (short for "kilobinary"), "mebi" ("megabinary"), "gibi" ("gigabinary") and "tebi" ("terabinary"), with respective symbols "kb", "Mb", "Gb" and "Tb",<ref name="iucr1995" /> for binary multipliers. The proposal suggested that the SI prefixes should be used only for powers of 10; so that a disk drive capacity of "500 gigabytes", "0.5 terabytes", "500&nbsp;GB", or "0.5&nbsp;TB" should all mean {{val|500|e=9|u=bytes}}, exactly or approximately, rather than {{nowrap|500 × 2<sup>30</sup>}} (=&nbsp;{{val|536870912000}}) or {{nowrap|0.5 × 2<sup>40</sup>}} (=&nbsp;{{val|549755813888}}).


The proposal was not accepted by IUPAC at the time, but was taken up in 1996 by the ] (IEEE) in collaboration with the ] (ISO) and ] (IEC). The prefixes "kibi", "mebi", "gibi" and "tebi" were retained, but with the symbols "Ki" (with capital "K"), "Mi", "Gi" and "Ti" respectively.<ref name="iucr1996" /><!-- The preceding reference is weak as it merely consists of IUPAC noting IEC's proposal, but it is apparently the only thing we have. Would be better to have a ref for the actual proposal -->
==== Optical discs ====


In January 1999, the IEC published this proposal, with additional prefixes "pebi" ("Pi") and "exbi" ("Ei"), as an international standard (] Amendment 2)<ref name="iec1999" /><!--- the preceding reference really needs more than just a quote. From what is it quoting? ---><ref name="iucr1999" /><!--- this reference is weak as it merely consists of the International Union of Crystallography reporting on IUPAC's reporting on the IEC standard(!) ---><ref name="IEC2000" /> The standard reaffirmed the BIPM's position that the SI prefixes should always denote powers of 10. The third edition of the standard, published in 2005, added prefixes "zebi" and "yobi", thus matching all then-defined SI prefixes with binary counterparts.<ref name="iec2005" />
] capacities are always given in binary units. A "700 MB" (or "80 minute") CD has a nominal capacity of about 700 ] (approx 730 MB).<ref></ref> However, the capacities of other ] storage media like ], ], ] are given in decimal units. A "4.7 GB" DVD has a nominal capacity of about 4.38 ].<ref></ref>


The harmonized ]/] ]:2008 standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005 (those defining prefixes for binary multiples). The only significant change is the addition of explicit definitions for some quantities.<ref name="niso2008" /><!--- once again, a link to a cite to the document, not to the actual ISO/IEC document. This is unavoidable as the documents in question are *not* freely available ---> In 2009, the prefixes kibi-, mebi-, etc. were defined by ] in their own right, independently of the kibibyte, mebibyte, and so on.
==== Buses ====


The BIPM standard JCGM 200:2012 "International vocabulary of metrology – Basic and general concepts and associated terms (VIM), 3rd edition" lists the IEC binary prefixes and states "SI prefixes refer strictly to powers of 10, and should not be used for powers of 2. For example, 1 kilobit should not be used to represent {{val|1024}} bits (2<sup>10</sup>&nbsp;bits), which is 1 kibibit."<ref name="jcgm2012" />
] clock speeds and therefore bandwidths are both given in decimal units. For example, "]" memory on a ] bus, transferring 8 bytes per cycle running with a clock speed of 200 MHz = 200,000,000 cycles per second has a bandwidth of 200,000,000 × 2 × 8 = 3,200,000,000 ]/s = 3.2 GB/s (about 2.98 ]/s).


The IEC 60027-2 standard recommended operating systems and other software were updated to use binary or decimal prefixes consistently, but incorrect usage of SI prefixes for binary multiples is still common. At the time, the IEEE decided that their standards would use the prefixes "kilo", etc. with their metric definitions, but allowed the binary definitions to be used in an interim period as long as such usage was explicitly pointed out on a case-by-case basis.<ref name="barr1997" />
=== Software ===


==== Command line interpreters ==== ==== Other standards bodies and organizations ====
The IEC standard binary prefixes are supported by other standardization bodies and technical organizations.


The United States ] (NIST) supports the ISO/IEC standards for
Some ]s have language-level support for binary prefix notation similar to the ] used in many ]s.
"Prefixes for binary multiples" and has a web page<ref name="NISTbin" /> documenting them, describing and justifying their use. NIST suggests that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced as ''bee''.<ref name="NIST2" /> NIST has stated the SI prefixes "refer strictly to powers of 10" and that the binary definitions "should not be used" for them.<ref name="taylo2008" />


As of 2014, the microelectronics industry standards body ] describes the IEC prefixes in its online dictionary, but acknowledges that the SI prefixes and the symbols "K", "M" and "G" are still commonly used with the binary sense for memory sizes.<ref name="jedec2021" /><ref name="JEDEC2014" />
In ] all binary prefixes are case-insensitive and used in the binary, power-of-1024 sense.
Example:


On 19 March 2005, the IEEE standard ] ("Prefixes for Binary Multiples") was elevated to a full-use standard by the IEEE Standards Association after a two-year trial period.<ref name="IEEE2003" /><ref name="IEEE2005" /> {{As of|2008|4|lc=on}}, the IEEE Publications division does not require the use of IEC prefixes in its major magazines such as ''Spectrum''<ref name="walli2008" /> or ''Computer''.<ref name ="gesch2007">{{Cite journal |last1=Gschwind |first1=Michael |title=An Open Source Environment for Cell Broadband Engine System Software |journal=Computer |volume=40 |issue=6 |pages=37–47 |publisher=IEEE Computer Society |date=June 2007 |doi = 10.1109/MC.2007.192 |last2=Erb |first2=David |last3=Manning |first3=Sid |last4=Nutter |first4=Mark |s2cid=10877922 |url=http://www.research.ibm.com/people/m/mikeg/papers/2007_ieeecomputer.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.research.ibm.com/people/m/mikeg/papers/2007_ieeecomputer.pdf |archive-date=2022-10-09 |url-status=live }} "The processor has a memory subsystem with separate first-level 32-Kbyte instruction and data caches, and a 512-Kbyte unified second-level cache." Authors are with IBM.</ref> <!-- and many of the IEEE technical journals allow the authors to select the units in their papers.{{Citation needed|date=May 2008}}-->
<source lang="text">
PS C:\>0.5kB
512


The ] (BIPM), which maintains the ] (SI), expressly prohibits the use of SI prefixes to denote binary multiples, and recommends the use of the IEC prefixes as an alternative since units of information are not included in the SI.<ref name="BIPM8web" /><ref name="BIPM8" />
PS C:\>1GB / 700MB
1.46285714285714


The ] (SAE) prohibits the use of SI prefixes with anything but a power-of-1000 meaning, but does not cite the IEC binary prefixes.<ref name="SAE2017" />
PS C:\>ls .\Users\root\Pictures\Pict*.jpeg | where {$_.length -gt 3.14mb}


The European Committee for Electrotechnical Standardization (]) adopted the IEC-recommended binary prefixes via the harmonization document HD&nbsp;60027-2:2003-03.<ref name="CENELEC2003" /> The European Union (EU) has required the use of the IEC binary prefixes since 2007.<ref name="CENELECxxxx" />
Directory: Microsoft.PowerShell.Core\FileSystem::C:\Users\root\Pictures


=== Current practice ===
Mode LastWriteTime Length Name
]
---- ------------- ------ ----
]'s partition editor uses IEC prefixes to display partition sizes. The total capacity of the 120&nbsp;×&nbsp;10<sup>9</sup>-byte disk is displayed as "111.79&nbsp;GiB".]]
-a--- 19.04.2008 20:11 3920613 Picture1.jpeg
]
-a--- 19.04.2008 20:16 6164149 Picture2.jpeg
-a--- 19.04.2008 20:19 4848501 Picture3.jpeg
</source>


Some computer industry participants, such as Hewlett-Packard (HP),<ref name="hpen2009" /> and IBM<ref name="resp2011" /><ref name="IBMaxxxx" /> have adopted or recommended IEC binary prefixes as part of their general documentation policies.
==== Adoption of IEC style ====


As of 2023, the use of SI prefixes with the binary meanings is still prevalent for specifying the capacity of the ] of computers, of ], ], ], and ] ] and ]s, and of the ] of ]s. For example, a "512-megabyte" or "512&nbsp;MB" memory module holds 512&nbsp;MiB; that is, 512&nbsp;×&nbsp;2<sup>20</sup> bytes, not 512&nbsp;×&nbsp;10<sup>6</sup> bytes.<ref name="customxxxx" /><ref name="HP2012" /><ref name="sony2017" /><ref name="forall2012" />
], the ] binary naming convention has been adopted by some, but is not used universally. Most{{Specify|date=January 2008}} publications, computer manufacturers and software companies are still using the traditional binary units defined in IEEE 100, ''The Authoritative Dictionary of IEEE Standards Terms'', Seventh Edition, 2000.<ref name=" IEEE100 "/>{{Dubious|date=March 2008}}


JEDEC continues to include the customary binary definitions of "kilo", "mega", and "giga" in the document ''Terms, Definitions, and Letter Symbols'',<ref name="JEDEC-terms" /> and, {{as of|2010|lc=yes}}, still used those definitions in their ].<ref name="JEDEC-ddr3" /><ref name="JEDEC-ddr2" /><ref name="JEDEC-configs" /><ref name="JEDEC-configs-toc" /><ref name="JEDEC-configs-terms" />
The binary convention is strongly supported by many standardization bodies and technical organizations, such as ], ], ], and ].<ref name="IEEE1541"> {{cite paper |doi=10.1109/IEEESTD.2003.94236 |title=IEEE Std 1541-2002: IEEE Trial-Use Standard for Prefixes for Binary Multiples |url=http://ieeexplore.ieee.org/servlet/opac?punumber=8450 |format=PDF |accessdate=2007-07-29 |date=] ] |version=Reaffirmed ] ]|quote=This standard is prepared with two goals in mind: (1) to preserve the SI prefixes as unambiguous decimal multipliers and (2) to provide alternative prefixes for those cases where binary multipliers are needed. The first goal affects the general public, the wide audience of technical and nontechnical persons who use computers without much concern for their construction or inner working. These persons will normally interpret kilo, mega, etc., in their proper decimal sense. The second goal speaks to specialists—the prefixes for binary multiples make it possible for persons who work in the information sciences to communicate with precision.}}
</ref><ref name="BIPM"/><ref name="NIST">
— The NIST Reference on Constants, Units, and Uncertainty
</ref><ref name="SAE">
— Section C.1.12 — SI prefixes
</ref>
The new binary prefixes have also been adopted by the European Committee for Electrotechnical Standardization (]) as the harmonization document HD&nbsp;60027-2:2003-03.<ref name="EUHD"> Information about the harmonization document (obtainable on order)</ref>
This document will be adopted as a ].<ref> Information about the EN standardization process</ref>


On the other hand, the SI prefixes with powers of ten meanings are generally used for the capacity of external storage units, such as ],<ref name="hita2009" /><ref name="sams2011" /><ref name="seag2017" /><ref name="toshi2009" /><ref name="WDC2005" /> ], and ],<ref name="sd-cap-disclaimer" /> except for some ] chips intended to be used as ]s. However, some disk manufacturers have used the IEC prefixes to avoid confusion.<ref name="toshi2017" /> The decimal meaning of SI prefixes is usually also intended in measurements of data transfer rates, and clock speeds.{{citation needed|date=August 2023}}
The prefixes are beginning to be used in technical articles and software where it is important to avoid ambiguity.<ref>e.g., The PC Guide magazine: </ref> Examples of software that use IEC standard prefixes (along with standard SI prefixes) include:


Some operating systems and other software use either the IEC binary multiplier symbols ("Ki", "Mi", etc.)<ref name="linux2001" /><ref name="ESR2012" /><ref name="ubuntu2012" /><ref name="ubuntu2012b" /><ref name="snow2009" /><ref name="apple2018" /> or the SI multiplier symbols ("k", "M", "G", etc.) with decimal meaning. Some programs, such as the ] ] command, let the user choose between binary or decimal multipliers. However, some continue to use the SI symbols with the binary meanings, even when reporting disk or file sizes. Some programs may also use "K" instead of "k", with either meaning.<ref>{{cite web | url=https://man7.org/linux/man-pages/man1/ls.1.html | title=Ls(1) – Linux manual page }}</ref>
{{col-begin}}
{{col-3}}
* The ]<ref>{{cite web
|url=http://www.annodex.net/cgi-bin/man/man2html?units+7
|title=UNITS
|accessdate=2007-05-20
|date=]
|work=]
|quote=When the Linux kernel boots and says <code>hda: 120064896 sectors (61473 MB) w/2048KiB Cache</code> the MB are megabytes and the KiB are kibibytes.
}}</ref>
* ]<ref>{{cite web
|url=http://www.gnu.org/software/coreutils/manual/html_node/Block-size.html#Block-size
|title=2.2 Block size
|accessdate=2007-05-20
|date=]
|work=] manual
|publisher=]
|quote=Integers may be followed by suffixes
that are upward compatible with the for decimal multiples and with the .
}}</ref>
* ]
* ]
* ]
* Flyspray<ref></ref>
* bugs.mysql.com<ref></ref>
* ]<ref>{{cite web
|url=http://sourceforge.net/project/shownotes.php?release_id=389304&group_id=115843
|title=gparted-0.2 changelog
|accessdate=2007-05-20
|date=]
|work=]
|quote=changed KB/MB/GB/TB to KiB/MiB/GiB/TiB after reading http://www.iec.ch/zone/si/si_bytes.htm
}}</ref>
* DFSee<ref></ref>
* disktype<ref></ref>
* raidutil<ref></ref>
* ]<ref></ref>
{{col-3}}
* ]
* ]
* ]<ref>{{cite web
|url=http://www.annodex.net/cgi-bin/man/man2html?8+ifconfig
|title=IFCONFIG
|accessdate=2007-05-20
|date=]
|work=]
|quote=Since net-tools 1.60-4 ifconfig is printing byte counters and human readable counters with IEC 60027-2 units. So 1 KiB are 2^10 byte.
}}</ref>
* GNOME Network<ref></ref>
* GNOME System Monitor
* Nautilus CD Burner
* ]<ref></ref>
* ]<ref></ref>
* ]<ref></ref>
* ]
* ]
* ]
{{col-3}}
* ]
* ]<ref>{{cite web
|url=http://dev.deluge-torrent.org/changeset/527
|title=Deluge changeset
|accessdate=2007-06-13
|quote=proper prefix for size
}}</ref>
* ]
* ]
* ]
* ]<ref></ref>
* ]<ref></ref>
* ]<ref></ref>
* ]<ref></ref>
* ]<ref>http://developer.pidgin.im/ticket/1684 Developer discussion</ref>
{{col-end}}


== Other uses ==
Note that one of the stated goals of the introduction of the binary prefixes was "to preserve the SI prefixes as unambiguous decimal multipliers."<ref name="IEEE1541"/> Programs such as ]/], ], and ] use SI prefixes with their decimal meaning.
While the binary prefixes are almost always used with the units of information, bits and bytes, they may be used with any other unit of measure, when convenient. For example, in ] one may need binary multiples of the frequency unit ] (Hz), for example the ] (KiHz), equal to {{val|1024|u=Hz}}.<ref name="pate2011" /><ref name="ains2022" />


== See also ==
<gallery perrow="6">
* ]
Image:Gnome Partition Editor showing 160 GB disk.png|]'s partition editor uses IEC prefixes to display partition sizes. The total capacity of the 160×10<sup>9</sup> byte disk is displayed as "149.05 ]"
* ]
Image:GNOME System Monitor memory size and network rate.png|GNOME's system monitor uses IEC prefixes to show memory size and networking data rate.
* ]
Image:Bittornado screenshot showing use of IEC and SI prefixes.png|] uses standard SI prefixes for data rates and IEC prefixes for file sizes
* ]
Image:Deluge_using_Si_prefix_for_wiki_CD.png|] uses IEC prefixes for data rates as well as file sizes
* ]
Image:Fdisk showing 160 GB disk.png|Linux's ] uses standard ]es to display a 160×10<sup>9</sup> byte disk as "160.0 GB"
{{clear}}
</gallery>


== Legal disputes == == References ==
{{reflist|refs=


<ref name="hpen2009">Hewlett-Packard (2009): ISS Technology Update – Hewlett Packard Enterprise, volume 9, issue 1, quote: 'To reduce confusion, vendors are pursuing one of two remedies: they are changing SI prefixes to the new binary prefixes, or they are recalculating the numbers as powers of ten. HP is considering modifying its storage utilities to report disk capacity with correct decimal and binary values side-by-side (for example, "300&nbsp;GB (279.4&nbsp;GiB)"), and report cache sizes with binary prefixes ("1&nbsp;GiB")'.</ref>
There have been two significant class action lawsuits against digital storage manufactures. One case involved flash memory and the other involved hard disk drives. Both were settled with the manufactures agreeing to clarify the storage capacity of their products on the consumer packaging. <!--See the settlements below-->


<ref name="suitxxxx">{{cite web | url = https://www.courthousenews.com/wp-content/uploads/2020/01/flashdrives.pdf | title = Order Granting Motion to Dismiss | publisher = ] | access-date = 2020-01-24 }}</ref>
=== Willem Vroegh v. Eastman Kodak Company ===


<ref name="sand2021">See also Dinan v. SanDisk LLC, No. 20-15287 (9th Cir. Feb. 11, 2021) https://scholar.google.com/scholar_case?case=16989791406584358656</ref>
On ], ], ] against Lexar Media, Dane–Elec Memory, ], ] Company, Kingston Technology Company, Inc., ] Products, Inc.; ] Inc., ], ], and Viking InterWorks alleging that their descriptions of the capacity of their ] cards were false and misleading.


<ref name="NIST1">{{cite web | url=http://physics.nist.gov/cuu/Units/prefixes.html | title = SI prefixes |author=<!--Not stated--> | website = The NIST Reference on Constants, Units, and Uncertainty: International System of Units (SI) | date = 13 January 2010 | publisher = ] | access-date = 2017-04-03}}</ref>
Vroegh claimed that a 256 MB Flash Memory Device had only 244 MB of accessible memory. "Plaintiffs allege that Defendants marketed the memory capacity of their products by assuming that one megabyte equals one million bytes and one gigabyte equals one billion bytes." The plaintiffs wanted to use the binary values 2<sup>20</sup> for megabyte and 2<sup>30</sup> for gigabyte. The plaintiffs acknowledged that the IEC and IEEE standards define a MB as one million bytes but stated that the industry has largely ignored the IEC standards.<ref name="Vreogh-3rd">{{cite web
| date = ] ]
| url = https://www.pddocs.com/FlashMemory/Documents/Vroegh%20Third%20Amended%20Complaint.pdf
| title = "Vreogh Third Amended Complaint (Case No. GCG-04-428953)"
| format = PDF
| work = pddocs.com
| publisher = Poorman-Douglas Corporation
| accessdate = 2007-09-09
}}</ref>


<ref name="frev1795">{{cite web |title=La Loi Du 18 Germinal An 3: Décision de tracer le mètre, unité fondamentale, sur une règle de platine. Nomenclature des " mesures républicaines ". Reprise de la triangulation. |language=fr |trans-title=The Law of 18 ], Year 3: Decision to draw the fundamental unit metre on a platinum ruler. Nomenclature of "Republican measures". Resumption of the triangulation. |work=L'Histoire Du Mètre |publisher=histoire.du.metre.free.fr |url=http://histoire.du.metre.free.fr/fr/Pages/Sommaire/06.htm |access-date=2015-10-12 |url-status=live |archive-url=https://web.archive.org/web/20221126164814/http://histoire.du.metre.free.fr/fr/Pages/Sommaire/06.htm |archive-date=2022-11-26 |quote=Art. 8. Dans les poids et mesures de capacité, chacune des mesures décimales de ces deux genres aura son double et sa moitié, afin de donner à la vente des divers objets toute la commodité que l'on peut désirer. Il y aura donc le double-litre et le demi-litre, le double-hectogramme et le demi-hectogramme, et ainsi des autres. |trans-quote=Art. 8. In the weights and measures of capacity, each of the decimal measures of these two kinds will have its double and its half, in order to give to the sale of the various articles all the convenience that one can desire. There will therefore be the double-litre and the half-litre, the double-hectogram and the half-hectogram, and so on.}}</ref>
The manufacturers agreed to clarify the flash memory card capacity on the packaging and web sites.<ref>http://www.sandisk.com/Assets/Categories/Products/sd_capacitydisclaimer.pdf</ref> The consumers could apply for "a discount of ten percent off a future online purchase from Defendants' Online Stores Flash Memory Device".<ref name="FMsettle-faq">{{cite web
| last = Safier
| first = Seth A.
| url = https://www.pddocs.com/FlashMemory/faq.aspx
| title = Frequently Asked Questions
| work = Flash Memory Settlement
| publisher = Poorman-Douglas Corporation
| accessdate = 2007-09-09
}}</ref>


<ref name="weik1961">{{cite journal |title = A Third Survey of Domestic Electronic Digital Computing Systems: Chapter III Analysis and Trends |quote = Of 187 different relevant systems, 131 utilize a straight binary system internally, whereas 53 utilize the decimal system (primarily binary coded decimal) and 3 systems utilize a binary coded alphanumeric system of notation. |journal = Ballistic Research Laboratories Report No. 1115 | first = Martin H. |last = Weik |date=March 1961 |page = 1027 |url = http://ed-thelen.org/comp-hist/BRL61analysis.html#STORAGE }} This lengthy report describes many of the early computers.</ref>
=== Orin Safier v. Western Digital Corporation ===


<ref name="blais1930">Hunting Trouble on 28 Megacycles, A. L. Blais, QST, January 1930.</ref>
On ], ], an action entitled "Orin Safier v. ] Corporation, et al.," was filed in the Superior Court for the City and County of San Francisco, Case No. CGC-05-442812. The case was subsequently moved to the Northern District of California, Case No. 05-03353 BZ.<ref name="wdc-safier-complaint">{{cite web
| last = Gutride
| first = Adam
| coauthors = Seth A. Safier
| date = ] ]
| url = http://www.wdc.com/settlement/docs/complaint.htm
| title = "Class Action Complaint"
| work = ''Orin Safier v. Western Digital Corporation''
| publisher = ]
| accessdate = 2007-09-09
}}</ref>


<ref name="real1959">{{Cite journal | last = Real | first = P. | title = A generalized analysis of variance program utilizing binary logic. | journal = ACM '59: Preprints of Papers Presented at the 14th National Meeting of the Association for Computing Machinery | pages = 78–1–78–5 |date=September 1959 | doi = 10.1145/612201.612294 | publisher = ACM Press | s2cid = 14701651 | quote = On a 32K core size 704 computer, approximately {{val|28000}} data may be analyzed, ... without resorting to auxiliary tape storage.| doi-access = free }} Note: the IBM 704 core memory units had 4096 36-bit words. Up to {{val|32768}} words could be installed</ref>
Although Western Digital maintained that their usage of units is consistent with "the indisputably correct industry standard for measuring and describing storage capacity", and that they "cannot be expected to reform the software industry", they agreed to settle in March 2006 with ], ] as the Final Approval hearing date.<ref name="wdc-safier-settle">{{cite web
| last = Zimmerman
| first = Bernard
| date = 2006
| url = http://www.wdc.com/settlement/docs/longform.htm
| title = "Notice of Class Action and Proposed Settlement"
| work = Orin Safier v. Western Digital Corporation
| publisher = ]
| accessdate = 2007-09-09
}}</ref>


<ref name="gruen1960">{{Cite journal | last1 =Gruenberger | first1 =Fred | title =Letters to the Editor | journal =Communications of the ACM | volume =3 | issue =10 |date=October 1960 | doi = 10.1145/367415.367419 | last2 =Burgess | first2 =C. R. | last3 =Gruenberger | first3 =Fred| s2cid =3199685 }} "The 8K core stores were getting fairly common in this country in 1954. The 32K store started mass production in 1956; it is the standard now for large machines and at least 200 machines of the size (or its equivalent in the character addressable machines) are in existence today (and at least 100 were in existence in mid-1959)." Note: The ] was a character addressable computer.</ref>
Western Digital offered to compensate customers with a free download of backup and recovery software valued at US$30. They also paid $500,000 in fees and expenses to San Francisco lawyers Adam Gutride and Seth Safier, who filed the suit.<ref></ref>


<ref name="amda1964">{{Cite journal | last =Amdahl | first = Gene M. | author-link = Gene Amdahl | title = Architecture of the IBM System/360 | journal =IBM Journal of Research and Development | volume =8 | issue =2 | publisher = IBM | year = 1964 | url = http://www.research.ibm.com/journal/rd/441/amdahl.pdf | doi = 10.1147/rd.82.0087 | pages=87–101}} Figure 1 gives storage (memory) capacity ranges of the various models in "Capacity 8-bit bytes, 1 K = 1024"</ref>
Western Digital had this footnote in their settlement. "Apparently, Plaintiff believes that he could sue an egg company for fraud for labeling a carton of 12 eggs a “dozen,” because some bakers would view a “dozen” as including 13 items."<ref name="Baskin-2006-02-01">{{cite web
| last = Baskin
| first = Scott D.
| date = ] ]
| url = http://www.wdc.com/settlement/docs/document20.htm
| title = "Defendant Western Digital Corporation's Brief in Support of Plaintiff's Motion for Preliminary Approval"
| work = ''Orin Safier v. Western Digital Corporation''
| publisher = ]
| accessdate = 2007-09-09
}}</ref>


<ref name="CDC7600">{{Cite book | author = Control Data Corporation | title = Control Data 7600 Computer System: Preliminary System Description |date=November 1968 | url = http://archive.computerhistory.org/resources/text/CDC/CDC.7600.1968.102646087.pdf |quote = One type, designated as the small core memory (SCM) is a many bank coincident current type memory with a total of 64K words of 60 bit length (K=1024). }}</ref>
The flash memory and hard disk manufacturers now have disclaimers on their packaging and web sites clarifying the formatted capacity of the flash memory<ref name="sd-cap-disclaimer"/>
or defining MB as 1 million bytes and 1 GB as 1 billion bytes.<ref name="wdc-CaviarSE16">{{cite web
| url = http://www.wdc.com/en/products/Products.asp?DriveID=301
| title = "WD Caviar SE16 SATA Hard Drives"
| work = Western Digital: Products
| publisher = ]
| accessdate = 2007-09-09
}}</ref>


<ref name="CDC1967">{{Cite book |author = Control Data Corporation |title = Control Data 6400/6500/6600 Computer Systems Reference Manual |year = 1965–1967 |pages = 2–1 |edition = Pub No. 60100000 |url = http://ed-thelen.org/comp-hist/CDC-6600-R-M.html#TOC/ |quote = Central Memory is organized into 32K, 65K, or 131K words (60-bit) in 8, 16, or 32 banks of 4096 words each. |access-date = 2013-11-07 |archive-url = https://web.archive.org/web/20140102194752/http://ed-thelen.org/comp-hist/CDC-6600-R-M.html#TOC/ |archive-date = 2014-01-02 }}</ref>
== See also ==


<ref name="frank1974">{{Cite journal |last = Frankenberg |first = Robert |title = All Semiconductor Memory Selected for New Minicomputer Series |journal = Hewlett-Packard Journal |volume = 26 |issue = 2 |pages = 15–20 |publisher = Hewlett-Packard |date = October 1974 |url = http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1974-10.pdf |access-date = 2007-06-18 |quote = 196K-word memory size |archive-date = 2007-11-29 |archive-url = https://web.archive.org/web/20071129060208/http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1974-10.pdf |url-status = dead }}</ref>
* ]
* ]
* ]
* ]
* ]
* ]
* ]-2
* ]


<ref name="HP1973">{{Cite journal | last = Hewlett-Packard | title =HP 3000 Configuration Guide | journal = HP 3000 Computer System and Subsystem Data | page = 59 |date = November 1973 | url = http://www.bitsavers.org/pdf/hp/3000/hp3000/5952-4500_optionsBrochure_Nov73.pdf |access-date=2010-01-22}}</ref>
=== Specific units of IEC 60027-2 A.2 ===


<ref name="horak2008">{{cite book|title=Webster's New World Telecom Dictionary|author=Ray Horak|page=271|publisher=]|year=2008|isbn=9780471774570|quote=In computing and storage systems, a kB (kiloByte) is actually 1,024 (2^10) bytes, since the measurement is based on a base 2, or binary, number system. The term kB comes from the fact that 1,024 is nominally, or approximately, 1,000.}}</ref>
These units have individual articles:


<ref name="dodd1997">{{cite book |title=The ACS style guide: a manual for authors and editors|author=Janet S. Dodd|page=124|publisher=]|year=1997|isbn=9780841234611|quote=kB (kilobyte; actually 1024 bytes) KB (kilobyte; kB is preferred)}}</ref>
{| width="100%"
|-
| valign="top" | {{Bitrates}}
| valign="top" | {{Quantities of bytes}}
| valign="top" | {{Quantities of bits}}
|}


<ref name="laver1989">{{cite book |title=Information Technology: Agent of Change|author=F. J. M. Laver|date=11 May 1989|page=35|publisher=]|isbn=978-0521350358|quote=when describing the performance of IT systems the larger units 'kilobytes' (kB) Strictly speaking, k means the 'binary thousand' 1024}}</ref>
== References ==


<ref name="liny1972">{{Cite journal|last1=Lin |first1=Yeong |title=Cost-performance evaluation of memory hierarchies |journal=IEEE Transactions on Magnetics |volume=8 |issue=3 |pages=390–392 |publisher=IEEE |date=September 1972 |quote=Also, random access devices are advantageous over serial access devices for backing store applications only when the memory capacity is less than 1&nbsp;Mbyte. For capacities of 4&nbsp;Mbyte and 16&nbsp;Mbyte serial access stores with shift register lengths of 256 bit and 1024 bit, respectively, look favorable. |doi=10.1109/TMAG.1972.1067329 |last2=Mattson |first2=R. |bibcode=1972ITM.....8..390L}}</ref>
{{reflist|2}}


<ref name="IBM1972">{{Cite book | last =IBM| title = System/370 Model 158 brochure | publisher = IBM | year = 1972 | url = http://archive.computerhistory.org/resources/text/IBM/IBM.370Mod158.1972.102646258.pdf | quote = All-monolithic storage ... (1024-bit NMOS) This new improvement of processor storage makes system expansion more economical. Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes. | id = G520-261871 }}</ref>
== Further reading ==


<ref name="bell1975">{{Cite journal | last = Bell | first = Gordon | title = Computer structures: What have we learned from the PDP-11? | journal = ISCA '76: Proceedings of the 3rd Annual Symposium on Computer Architecture | pages = 1–14 | publisher = ACM Press |date=November 1975 | url = http://research.microsoft.com/~gbell/Digital/Bell_Strecker_What_we%20_learned_fm_PDP-11c%207511.pdf | doi = 10.1145/800110.803541 | s2cid = 14496112 | quote = memory size (8k bytes to 4 megabytes). }}</ref>
* {{cite web|url=http://www.iec.ch/zone/si/si_bytes.htm|title=When is a kilobyte a kibibyte? And an MB an MiB?|publisher=International Electrotechnical Commission|date=]}} — An introduction to binary prefixes

<ref name="IBM1956">{{cite web |url=http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html |archive-url=https://web.archive.org/web/20050409064858/http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html |url-status=dead |archive-date=9 April 2005 |work=IBM Archives |title=IBM 350 disk storage unit |author=IBM Corporation|date=23 January 2003 }}</ref>

<ref name="CDC1974">The unambiguously uses MB to characterize HDD capacity in millions of bytes</ref>

<ref name="RDD1977">1977 Disk/Trend Report – Rigid Disk Drives, published June 1977</ref>

<ref name="seag1982">{{cite book |url = http://maben.homeip.net/static/S100/seagate/disks/Seagate%20ST412%20OEM%20Manual%201982.pdf |title = ST506/412 OEM Manual |author = Seagate Corporation |date = April 1982 |page = 3 |access-date = 2016-09-06 |archive-url = https://web.archive.org/web/20161008003923/http://maben.homeip.net/static/S100/seagate/disks/Seagate%20ST412%20OEM%20Manual%201982.pdf |archive-date = 2016-10-08 }}</ref>

<ref name="CSN1984">IBM Tells MiniScribe It Is Cutting Back On Winchester Orders, Computer System News, 1 Jan 1984, p. 1</ref>

<ref name="mall2011">{{cite web|last=Mellor |first=Chris |url=https://www.theregister.co.uk/2011/04/06/oldest_seagate_drive_in_uk/ |title=It's the oldest working Seagate drive in the UK |publisher=The Register |date=2011-04-06 |access-date=2012-01-26}}</ref>

<ref name="seaga2011">, 100628561, Rev D, March 2011, sec 5.2.3, p. 10 (18th page of the pdf), states the drive's sustained transfer speed as "89 to 160 ]/s" on one line, and "93 to 168&nbsp;MB/s" on the next line.</ref>

<ref name="seag2010">{{cite web|title=Marketing Bulletin: Advanced Format 4K Sector Transition Frequently Asked Questions|url=http://www.seagate.com/docs/pdf/whitepaper/mb604_4k_transition_faq.pdf|publisher=]|archive-url=https://web.archive.org/web/20100715030704/http://www.seagate.com/docs/pdf/whitepaper/mb604_4k_transition_faq.pdf|archive-date=15 July 2010}}</ref>

<ref name="hita2007">{{cite web |url=http://www.pcworld.com/article/id,128400-page,1/article.html |title=Hitachi Introduces 1-Terabyte Hard Drive |work=PC World |date=2007-01-04 |access-date=2010-02-04 |archive-date=2007-01-12 |archive-url=https://web.archive.org/web/20070112044932/http://www.pcworld.com/article/id,128400-page,1/article.html }}</ref>

<ref name="ansi1986">{{Cite book|date=30 October 1986 |quote=kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 2<sup>10</sup>, or 1024. mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 2<sup>20</sup>, or 1048576. |doi=10.1109/IEEESTD.1986.79649 |isbn=0-7381-4541-6 |title=IEEE Standard Glossary of Mathematics of Computing Terminology }}</ref>

<ref name="ieee1992">{{Cite book|date=22 July 1992 |quote=Kbyte. Kilobyte. Indicates 2<sup>10</sup> bytes. Mbyte. Megabyte. Indicates 2<sup>20</sup>bytes. Gbyte is used in the Foreword. |doi=10.1109/IEEESTD.1992.106981 |isbn=0-7381-4336-7 |title=IEEE Standard Control and Status Register (CSR) Architecture for Microcomputer Buses }}</ref>

<ref name="webster">{{cite web|url=http://www.m-w.com/dictionary/Megabyte|title=Definition of megabyte|website=M-w.com|access-date=30 December 2017}}</ref>

<ref name="metadict">{{cite web|url=http://dictionary.reference.com/browse/Megabyte|title=Definitions of Megabyte|website=Dictionary.reference.com|access-date=30 December 2017}}</ref>

<ref name="oxford">{{cite web|url=http://www.askoxford.com/concise_oed/megabyte?view=uk|archive-url=https://web.archive.org/web/20050525164142/http://www.askoxford.com/concise_oed/megabyte?view=uk|url-status=dead|archive-date=25 May 2005|title=AskOxford: megabyte|website=Askoxford.com|access-date=30 December 2017}}</ref>

<ref name="ieee1994">{{Cite book | date=24 June 1994 | quote= gigabyte (gig, GB). This term may mean either a) {{val|1000000000}} bytes or b) 2<sup>30</sup> bytes. ... As used in this document, the terms kilobyte (kB) means 2<sup>10</sup> or 1024 bytes, megabyte (MB) means 1024 kilobytes, and gigabyte (GB) means 1024 megabytes.|doi=10.1109/IEEESTD.1995.79522 |isbn=1-55937-492-6 | title=IEEE Standard Glossary of Computer Hardware Terminology }}</ref>

<ref name="ieee2000">{{Cite book|author=Institute of Electrical and Electronics Engineers |title=100-2000 |author-link=Institute of Electrical and Electronics Engineers |publisher=IEEE Computer Society Press |year=2000 |isbn=978-0-7381-2601-2 |doi=10.1109/IEEESTD.2000.322230 |url=https://repositorio.unal.edu.co/handle/unal/79391 }} "kB See kilobyte." "Kbyte Kilobyte. Indicates 2<sup>10</sup> bytes." "Kilobyte Either 1000 or 2<sup>10</sup> or 1024 bytes." The standard also defines megabyte and gigabyte with a note that an alternative notation for base 2 is under development.</ref>

<ref name="wdc2007">{{cite web | url = http://www.wdc.com/en/products/Products.asp?DriveID=301 | title = WD Caviar SE16 SATA Hard Drives | work = Western Digital: Products | publisher = ] | access-date = 2007-09-09 | archive-url = https://web.archive.org/web/20070902080558/http://www.wdc.com/en/products/products.asp?driveid=301 | archive-date = 2007-09-02 }}</ref>

<ref name="flash2016">{{cite web | url = http://forum.corsair.com/v3/showthread.php?t=33071 | title = Jack Flash F.A.Q. | publisher = ] | access-date = 2014-06-20 | quote = the industry-standard definition of a megabyte (MByte) for flash devices is one million (1,000,000) bytes, where the operating system uses two to the twentieth power, or 1,048,576 bytes. Similarly, for a gigabyte (GByte), the number is 1,000,000,000 and 1,073,741,824 respectively. | archive-date = 2016-03-05 | archive-url = https://web.archive.org/web/20160305080304/http://forum.corsair.com/v3/showthread.php?t=33071 }}</ref>

<ref name="sand2013">{{cite web |url=http://www.sandisk.com/media/416788/80-11-01707_rev1_datasheet_ultracf_r1.pdf |title=SanDisk Ultra CompactFlash cards |publisher=] |access-date=2014-06-20 |archive-url=https://web.archive.org/web/20130810032314/http://www.sandisk.com/media/416788/80-11-01707_rev1_datasheet_ultracf_r1.pdf |archive-date=2013-08-10 }}</ref>

<ref name="vreo2005">{{cite web|date=10 March 2005 |url=https://www.pddocs.com/FlashMemory/Documents/Vroegh%20Third%20Amended%20Complaint.pdf |title=Vreogh Third Amended Complaint (Case No. GCG-04-428953) |work=pddocs.com |publisher=Poorman-Douglas Corporation |access-date=2007-09-09 |archive-url=https://web.archive.org/web/20080309143513/https://www.pddocs.com/FlashMemory/Documents/Vroegh%20Third%20Amended%20Complaint.pdf |archive-date=9 March 2008 }}</ref>

<ref name="sand2012">{{cite web |title=Why is the capacity of my Secure Digital memory card (as reported by many operating systems) different than the capacity that is listed on its label? |url=http://www.sandisk.com/Assets/Categories/Products/sd_capacitydisclaimer.pdf|archive-url=https://web.archive.org/web/20120413100902/http://www.sandisk.com/Assets/Categories/Products/sd_capacitydisclaimer.pdf|archive-date=13 April 2012|date=13 April 2012|website=Sandisk.com|access-date=30 December 2017}}</ref>

<ref name="safi2007">{{cite web|last=Safier |first=Seth A. |url=https://www.pddocs.com/FlashMemory/faq.aspx |title=Frequently Asked Questions |work=Flash Memory Settlement |publisher=Poorman-Douglas Corporation |access-date=2007-09-09 |archive-url=https://web.archive.org/web/20070928013731/https://www.pddocs.com/FlashMemory/faq.aspx |archive-date=28 September 2007 }}</ref>

<ref name="gutr2006">{{cite web | last = Gutride | first = Adam | author2 = Seth A. Safier | date = 29 March 2006 | url = http://www.wdc.com/settlement/docs/complaint.htm | title = Class Action Complaint | work = Orin Safier v. Western Digital Corporation | publisher = ] | access-date = 2007-09-09 | archive-url = https://web.archive.org/web/20071016171124/http://wdc.com/settlement/docs/complaint.htm | archive-date = 16 October 2007 }}</ref>

<ref name="zimm2006">{{cite web | last = Zimmerman | first = Bernard | year = 2006 | url = http://www.wdc.com/settlement/docs/longform.htm | title = Notice of Class Action and Proposed Settlement | work = Orin Safier v. Western Digital Corporation | publisher = ] | access-date = 2007-09-09 | archive-url = https://web.archive.org/web/20070922234210/http://www.wdc.com/settlement/docs/longform.htm | archive-date = 2007-09-22 }}</ref>

<ref name="betaxxxx">{{cite web|url=http://www.betanews.com/article/Western_Digital_Settles_Capacity_Suit/1151510648|title=Western Digital Settles Capacity Suit|website=Betanews.com|access-date=30 December 2017|date=28 June 2006}}</ref>

<ref name="reim2006">{{cite web |url=https://arstechnica.com/old/content/2006/06/7174.ars |title=Western Digital settles drive size lawsuit |author=Jeremy Reimer |date=2006-06-30 |publisher=Ars Technica LLC |access-date=2010-02-10 }}</ref>

<ref name="wdc2010">{{cite web |url=http://www.wdc.com/settlement/docs/longform.htm |title=NOTICE OF CLASS ACTION AND PROPOSED SETTLEMENT ("NOTICE") |author=Western Digital Corporation |year=2006 |access-date=2010-02-10 |archive-url=https://web.archive.org/web/20100507132711/http://www.wdc.com/settlement/docs/longform.htm |archive-date=2010-05-07 }}</ref>

<ref name="bask2006">{{cite web | last = Baskin | first = Scott D. | date = 1 February 2006 | url = http://www.wdc.com/settlement/docs/document20.htm | title = "Defendant Western Digital Corporation's Brief in Support of Plaintiff's Motion for Preliminary Approval" | work = Orin Safier v. Western Digital Corporation | publisher = ] | access-date = 2007-09-09 }}</ref>

<ref name="seagb2011">{{cite web | url = http://www.harddrive-settlement.com | title = Settlement Website for Cho v. Seagate Technology (US) Holdings, Inc. | access-date = 2011-04-12 | archive-url = https://web.archive.org/web/20190118155341/http://www.harddrive-settlement.com/ | archive-date = 18 January 2019 }}</ref>

<ref name="suitbxxxx">{{cite web | url = https://www.courthousenews.com/wp-content/uploads/2020/01/flashdrives.pdf | title = Order Granting Motion to Dismiss | publisher = ] | access-date = 2020-01-24 }}</ref>

<ref name="morr1968">{{Cite journal |title=Letters to the editor: Abbreviations for computer and memory sizes |author= Donald R. Morrison, ] |journal= Communications of the ACM |volume=11 |issue=3 |date=March 1968 |page=150 |doi=10.1145/362929.362962|s2cid= 22934466 |doi-access=free}}</ref>

<ref name="give1968">{{Cite journal |title=Letters to the editor: proposed abbreviation for 1024: bK |author= Wallace Givens, Applied National Lab |journal= Communications of the ACM |volume=11 |issue=6 |date=June 1968 |page=391 |doi=10.1145/363347.363351|s2cid= 22205692 |doi-access=free}}</ref>

<ref name="mart1968">{{cite journal | title=Letters to the editor: On binary notation | first=Bruce Alan | last=Martin | publisher=] | journal=] | volume=11 | issue=10 | date=October 1968 | page=658 | doi=10.1145/364096.364107| s2cid=28248410 | doi-access=free }}</ref>

<ref name="schw1993">{{cite book|title=HP16C Emulator Library for the HP48S/SX|first1=Jake|last1=Schwartz|first2=Rick|last2=Grevelle|date=2003-10-20|orig-date=1993<!-- 1993-04 -->|edition=1|version=1.20|url=http://www.pahhc.org/mul8r.htm|access-date=2015-08-15}}</ref>

<ref name="kuhn1996">{{cite web |url=http://www.cl.cam.ac.uk/~mgk25/information-units.txt |title=Standardized units for use in information technology |author-first=Markus |author-last=Kuhn|author-link=Markus Kuhn (computer scientist) |date=29 December 1996}}</ref>

<ref name="knuth2016">'' {{webarchive|url=https://web.archive.org/web/20160305014709/http://www-cs-staff.stanford.edu/~knuth/fasc1.ps.gz |date=2016-03-05 }}'' Volume 1, ], pp. 24 and 94</ref>

<ref name="knuth1999">{{cite web|url=https://www-cs-faculty.stanford.edu/~knuth/news99.html |title=Knuth: Recent News (1999) |publisher=Cs-staff.stanford.edu |access-date=2012-01-26}}</ref>

<ref name="iucr1995">{{cite web |title=IUCr annual report for 1995 |publisher=] |author=IUCr IUPAC Interdivisional Committee on Nomenclature and Symbols (IDCNS) |type=Report |date=1997-02-13 |orig-date=1995 |url=http://ww1.iucr.org/cexec/rep95/idcns.htm |access-date=2012-01-26 |url-status=dead |archive-url=https://web.archive.org/web/20090827091437/http://ww1.iucr.org/cexec/rep95/idcns.htm |archive-date=2009-08-27}}</ref>

<ref name="iucr1996">{{cite web |title=(IUCr) 1996 Report – IUPAC Interdivisional Committee on Nomenclature and Symbols (IDCNS) |type=Report |publisher=] |date=1997-02-14 |orig-date=1996 |url=http://www.chester.iucr.org/iucr-top/cexec/rep96/idcns.htm |access-date=2012-01-26 |url-status=dead |archive-url=https://web.archive.org/web/20130613121942/http://www.chester.iucr.org/iucr-top/cexec/rep96/idcns.htm |archive-date=2013-06-13}}</ref>

<ref name="barr1997">{{cite journal |author-first=Bruce |author-last=Barrow |title=A Lesson in Megabytes |journal=IEEE Standards Bearer |volume=11 |date=January 1997 |orig-date=1996 |publisher=] |page=5 |url=https://www.thierry-lequeu.fr/data/PELS/Comm/Publications/Newsletter/9704/STORY18.HTML |access-date=2022-12-24 |url-status=live |archive-url=https://web.archive.org/web/20220528124411/https://www.thierry-lequeu.fr/data/PELS/Comm/Publications/Newsletter/9704/STORY18.HTML |archive-date=2022-05-28}}</ref>

<ref name="iec1999">"These prefixes for binary multiples, which were developed by IEC Technical Committee (TC) 25, Quantities and units, and their letter symbols, with the strong support of the International Committee for Weights and Measures (CIPM) and the IEEE, were adopted by the IEC as Amendment 2 to IEC International Standard IEC 60027-2: Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics."</ref>

<ref name="iucr1999">{{cite journal|url=http://journals.iucr.org/a/issues/2000/06/00/es0288/es0288bdy.html#SEC15.1 |title=IUCR 1999 report on IUPAC Interdivisional Committee on Nomenclature and Symbols |journal=Acta Crystallographica Section A: Foundations of Crystallography |date=November 2000 |volume=56 |issue=6 |pages=609–642 |publisher=Journals.iucr.org |doi=10.1107/S0108767300012873 |pmid=11058849 |access-date=2012-01-26|doi-access=free }}</ref>

<ref name="IEC2000">IEC 60027-2 (2000-11) Ed. 2.0</ref>

<ref name="iec2005">{{cite press release|date=2005-08-15 |title=HERE COME ZEBI AND YOBI |publisher=International Electrotechnical Commission |url=http://www.iec.ch/news_centre/release/nr2005/nr2005.htm |archive-url=https://archive.today/20070611071833/http://www.iec.ch/news_centre/release/nr2005/nr2005.htm |archive-date=11 June 2007 }}</ref>

<ref name="niso2008">{{cite web |url=http://www.niso.org/publications/newsline/2008/newslinemay2008.htm#Spec4 |title=niso, New Specs and Standards |publisher=Niso.org |access-date=2012-01-26 |archive-url=https://web.archive.org/web/20081208131408/http://www.niso.org/publications/newsline/2008/newslinemay2008.htm#Spec4 |archive-date=2008-12-08 }}</ref>

<ref name="jcgm2012">{{cite web|url=http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf |archive-date=2022-10-09 |url-status=live|title=International vocabulary of metrology – Basic and general concepts and associated terms (VIM)|edition=3rd|website=Bipm.org|access-date=30 December 2017}}</ref>

<ref name="BIPM2022">{{cite web |title=List of Resolutions for the 27th meeting of the General Conference on Weights and Measures |url=https://www.bipm.org/documents/20126/64811223/Resolutions-2022.pdf |archive-url=https://web.archive.org/web/20221118153958/https://www.bipm.org/documents/20126/64811223/Resolutions-2022.pdf |archive-date=2022-11-18 |url-status=live |date=2022-11-18 |access-date=2022-11-18 }}</ref>

<ref name="gibn2022">{{cite journal |title=How many yottabytes in a quettabyte? Extreme numbers get new names |author-last=Gibney |author-first=Elizabeth |date=2022-11-18 |journal=] |volume= |issue= |pages= |doi=10.1038/d41586-022-03747-9 |pmid=36400954 |s2cid=253671538 |url=https://www.nature.com/articles/d41586-022-03747-9 |access-date=2022-11-21}}</ref>

<ref name="brown2023">{{cite journal |title=A further short history of the SI prefixes |journal=] |department=Letter to the editor |author-first=Richard J. C. |author-last=Brown |date=2023 |orig-date=2022-02-08, 2022-04-01, 2022-11-24 |volume=60 |issue=1 |page=013001 |publisher=] & ] |id=013001 |doi=10.1088/1681-7575/ac6afd |bibcode=2023Metro..60a3001B |s2cid=253966045 |doi-access=free }} (1+4 pages)</ref>

<ref name="brown2022">{{cite journal |title=Reply to 'Facing a shortage of the Latin letters for the prospective new SI symbols: alternative proposal for the new SI prefixes' |author-last=Brown |author-first=Richard J. C. |date=2022-04-27 |journal={{ill|Accreditation and Quality Assurance|de}} |volume=27 |issue= 3|pages=143–144 |doi=10.1007/s00769-022-01499-7|s2cid=248397680 }}</ref>

<ref name="NISTbin"></ref>

<ref name="NIST2">{{cite web | url = http://physics.nist.gov/cuu/Units/binary.html | title = International System of Units (SI): Prefixes for binary multiples | work = The NIST Reference on Constants, Units, and Uncertainty | publisher = ] | access-date = 2007-09-09 }}</ref>

<ref name="taylo2008">{{Cite book |author=Barry N. Taylor & Ambler Thompson Ed. |title=The International System of Units (SI) |url=http://physics.nist.gov/Pubs/SP330/sp330.pdf |access-date=2010-04-27 |publisher=National Institute of Standards and Technology |location=Gaithersburg, MD |page=29 |year=2008 |archive-date=2018-12-25 |archive-url=https://web.archive.org/web/20181225010952/https://physics.nist.gov/Pubs/SP330/sp330.pdf }}</ref>

<ref name="jedec2021">{{cite web|title=mega (M) (as a prefix to units of semiconductor storage capacity)|url=http://www.jedec.org/standards-documents/dictionary/terms/mega-m-prefix-units-semiconductor-storage-capacity|website=JEDEC – Global Standards for the Microelectronics Industry|access-date=14 April 2021|quote = "The definitions of kilo, giga, and mega based on powers of two are included only to reflect common usage."}}</ref>

<ref name="JEDEC2014">{{cite book | title = Low Power Double Data Rate 4 (LPDDR4) JESD209-4 | publisher = JEDEC Solid State Technology Association | date = August 2014 | page = 7 | url = http://www.jedec.org/standards-documents/results/jesd79-4%20ddr4 | quote = These devices contain the following number of bits: 4Gb has 4,294,967,296 bits ... 32Gb has 34,359,738,368 bits}} Free registration required to download the standard.</ref>

<ref name="IEEE2003">{{Cite book|doi=10.1109/IEEESTD.2003.94236 |url=http://ieeexplore.ieee.org/servlet/opac?punumber=8450 |archive-url=https://web.archive.org/web/20121014151530/http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?reload=true&punumber=8450 |archive-date=2012-10-14 |access-date=2007-07-29 |date=12 February 2003 |version=Reaffirmed 27 March 2008 |quote=This standard is prepared with two goals in mind: (1) to preserve the SI prefixes as unambiguous decimal multipliers and (2) to provide alternative prefixes for those cases where binary multipliers are needed. The first goal affects the general public, the wide audience of technical and nontechnical persons who use computers without much concern for their construction or inner working. These persons will normally interpret kilo, mega, etc., in their proper decimal sense. The second goal speaks to specialists – the prefixes for binary multiples make it possible for persons who work in the information sciences to communicate with precision. |isbn=978-0-7381-3385-0 |title=1541-2002 }}</ref>

<ref name="IEEE2005">{{cite web|url=http://standards.ieee.org/board/rev/305agenda.html |title=IEEE-SA Standards Board Standards Review Committee (RevCom) Meeting Agenda |access-date=2007-02-25 |date=2005-03-19 |quote='''1541-2002''' (SCC14) IEEE Trial-Use Standard for Prefixes for Binary Multiples '''' <u>Recommendation</u>: Elevate status of standard from trial-use to full-use. Editorial staff will be notified to implement the necessary changes. The standard will be due for a maintenance action in 2007. |archive-url=https://web.archive.org/web/20070922215418/http://standards.ieee.org/board/rev/305agenda.html |archive-date=22 September 2007 }}</ref>

<ref name="walli2008">{{Cite journal |last=Wallich |first=Paul |title=Tools & toys: Hacking the Nokia N800 |journal=IEEE Spectrum |volume=45 |issue=4 |page=25 |date=April 2008 |doi=10.1109/MSPEC.2008.4476441 |s2cid=20129812 }} ''"A lot can happen in a decade. You can hold the Nokia N800 in your hand, yet it's a near-exact match for a high-end desktop PC from 10 years ago. It has a 320-megahertz processor, 128 megabytes of RAM, and a few gigabytes of available mass storage."''</ref>

<ref name="BIPM8web">{{cite web |url=http://www.bipm.org/en/si/prefixes.html |title=BIPM – SI prefixes|website=Bipm.org|access-date=30 December 2017}}</ref>

<ref name="BIPM8">{{Cite book |title=The International System of Units (SI) |chapter-url=http://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf |archive-url=https://web.archive.org/web/20060813144253/http://www.bipm.org/utils/common/pdf/si_brochure_8.pdf |archive-date=2006-08-13 |url-status=live |access-date=2007-02-25 |edition=8th |year=2006 |publisher=STEDI Media |location=Paris |language=fr, en |isbn=978-92-822-2213-3 |page=127 |chapter=§3.1 SI prefixes |quote= These SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The IEC has adopted prefixes for binary powers in the international standard IEC 60027-2: 2005, third edition, ''Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics''. The names and symbols for the prefixes corresponding to 2<sup>10</sup>, 2<sup>20</sup>, 2<sup>30</sup>, 2<sup>40</sup>, 2<sup>50</sup>, and 2<sup>60</sup> are, respectively: kibi, Ki; mebi, Mi; gibi, Gi; tebi, Ti; pebi, Pi; and exbi, Ei. Thus, for example, one kibibyte would be written: 1&nbsp;KiB = 2<sup>10</sup>&nbsp;B = 1024&nbsp;B, where B denotes a byte. Although these prefixes are not part of the SI, they should be used in the field of information technology to avoid the incorrect usage of the SI prefixes. |author=Bureau International des Poids et Mesures.}}</ref>

<ref name="SAE2017">{{cite web|url=http://www.sae.org/standardsdev/tsb/tsb003.pdf#page=33 |archive-url=https://ghostarchive.org/archive/20221009/http://www.sae.org/standardsdev/tsb/tsb003.pdf#page=33 |archive-date=2022-10-09 |url-status=live|format=PDF|title=Rules for SAE Use of SI (Metric) Units] – Section C.1.12 – SI prefixes|website=Sae.org|access-date=30 December 2017}}</ref>

<ref name="CENELEC2003">{{Cite web|url=http://www.cenelec.eu/dyn/www/f?p=104:110:1546953662480229::::FSP_PROJECT,FSP_LANG_ID:15306,25|archive-url=https://archive.today/20130213052907/http://www.cenelec.eu/dyn/www/f?p=104:110:1546953662480229::::FSP_PROJECT,FSP_LANG_ID:15306,25|archive-date=2013-02-13|title = CENELEC – Standards Development – List of Technical Bodies}}</ref>

<ref name="CENELECxxxx">{{Cite web|url=http://www.cenelec.eu/dyn/www/f?p=104:110:6177007965168887::::FSP_PROJECT,FSP_LANG_ID:20776,25|archive-url=https://archive.today/20120722151947/http://www.cenelec.eu/dyn/www/f?p=104:110:6177007965168887::::FSP_PROJECT,FSP_LANG_ID:20776,25|archive-date=2012-07-22|title = CENELEC – Standards Development – List of Technical Bodies}}</ref>

<ref name="customxxxx">As used in this article, the term '''customary binary prefix''' or similar refers to prefixes such as kilo, mega, giga, etc., borrowed from the similarly named ]es but used to denote a power of 1024.</ref>

<ref name="HP2012">{{cite web|url=http://welcome.hp.com/country/us/en/welcome.html |title=Hewlett-Packard |publisher=Welcome.hp.com |access-date=2012-01-26}}</ref>

<ref name="sony2017">{{cite web|url=http://www.sonystyle.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10551&storeId=10151&langId=-1&categoryId=16155&SR=nav:shop:computers:desktops:ss&ref=http://www.sony.com/index.php|title=Consumer Electronics – Sony US|website=Sonystyle.com|access-date=30 December 2017|archive-date=2011-06-16 |archive-url=https://web.archive.org/web/20110616080047/http://www.sonystyle.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10551&storeId=10151&langId=-1&categoryId=16155&SR=nav%3Ashop%3Acomputers%3Adesktops%3Ass&ref=http%3A%2F%2Fwww.sony.com%2Findex.php}}</ref>

<ref name="forall2012">{{cite web|url=http://www.4allmemory.com/index.cfm?fuseaction=search.rdram_rambus_pc1066 |title=4AllMemory.com |publisher=4AllMemory.com |access-date=2012-01-26}}</ref>

<ref name="linux2001">{{cite web |url=http://www.annodex.net/cgi-bin/man/man2html?units+7 |title=Units |access-date=2007-05-20 |date=2001-12-22 |work=] |quote=When the Linux kernel boots and says <code>hda: 120064896 sectors (61473&nbsp;MB) w/2048KiB Cache</code> the MB are megabytes and the KiB are kibibytes. |url-status=usurped |archive-url=https://web.archive.org/web/20070902124532/http://www.annodex.net/cgi-bin/man/man2html?units+7 |archive-date=2 September 2007 }}</ref>

<ref name="ESR2012">{{cite web|url=https://lwn.net/2002/0103/a/esr-kibi.php3 |title=ESR post on LKML |publisher=Lwn.net |access-date=2012-01-26}}</ref>

<ref name="ubuntu2012">{{cite web|url=http://www.neowin.net/news/ubuntu-implements-units-policy-will-switch-to-base-10-units-in-future-release |title=Ubuntu implements units policy, will switch to base-10 units in future release |publisher=Neowin.net |access-date=2012-01-26}}</ref>

<ref name="ubuntu2012b">{{cite web|url=https://wiki.ubuntu.com/UnitsPolicy |title=UnitsPolicy – Ubuntu Wiki |publisher=Wiki.ubuntu.com |access-date=2012-01-26}}</ref>

<ref name="snow2009">{{cite magazine |url=http://www.macworld.co.uk/mac/news/index.cfm?RSS&NewsID=27034 |title=Snow Leopard's new maths |magazine=Macworld |date=2009-08-28 |access-date=2011-04-13 }}{{Dead link|date=May 2021 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

<ref name="apple2018">{{cite web |url=https://support.apple.com/en-ca/HT201402 |title=How iOS and macOS report storage capacity |publisher=Apple Inc |date=2018-02-27 |access-date=2021-06-27}}</ref>

<ref name="JEDEC-terms">{{cite web | author = JEDEC Solid State Technology Association | title = JEDEC Standard No. 100B.01 – Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits | date = December 2002 | page = 8 | url = http://www.jedec.org/download/search/JESD100B01.pdf | access-date = 2010-03-07 | quote = The definitions of kilo, giga, and mega based on powers of two are included only to reflect common usage. IEEE/ASTM SI 10-1997 states "This practice frequently leads to confusion and is deprecated." }} (Requires free registration and login.)</ref>

<ref name="JEDEC-ddr3">{{cite web |title=DDR3 SDRAM Standard |author=JEDEC |date = September 2009|access-date=2010-02-04 |url=http://www.jedec.org/standards-documents/docs/jesd-79-3d }}</ref>

<ref name="JEDEC-ddr2">{{cite web |title=DDR2 SDRAM Standard |author=JEDEC |date = November 2009|access-date=2010-02-04 |url=http://www.jedec.org/standards-documents/docs/jesd-79-2e }}</ref>

<ref name="JEDEC-configs">{{cite web |title=Memory Configurations |author=JEDEC |access-date=2010-02-04 |url=http://www.jedec.org/standards-documents/technology-focus-areas/memory-configurations-jesd21-c }}</ref>

<ref name="JEDEC-configs-toc">{{cite web |title=Memory Configurations Table of Contents |author=JEDEC |access-date=2010-02-04 |url=http://www.jedec.org/sites/default/files/21C_TOCR18.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.jedec.org/sites/default/files/21C_TOCR18.pdf |archive-date=2022-10-09 |url-status=live }}</ref>

<ref name="JEDEC-configs-terms">{{cite web |title=Terms and Definitions |author=JEDEC |access-date=2010-02-04 |url=http://www.jedec.org/sites/default/files/2_00R19.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.jedec.org/sites/default/files/2_00R19.pdf |archive-date=2022-10-09 |url-status=live }}</ref>

<ref name="hita2009">{{dead link|date=October 2015}}{{cbignore}}</ref>

<ref name="sams2011">{{cite web|url=http://www.samsung.com/global/business/hdd/faqView.do?b2b_bbs_msg_id=167 |archive-url=https://web.archive.org/web/20110616021347/http://www.samsung.com/global/business/hdd/faqView.do?b2b_bbs_msg_id=167 |archive-date=2011-06-16 |title=FAQs|website=Samsung.com |access-date=30 December 2017}}</ref>

<ref name="seag2017">{{cite web |url=http://www.seagate.com/docs/pdf/whitepaper/storage_solutions_guide.pdf |title=Storage Solutions Guide |website=Seagate |access-date=2010-03-04 |archive-url=https://web.archive.org/web/20100331115539/http://www.seagate.com/docs/pdf/whitepaper/storage_solutions_guide.pdf |archive-date=2010-03-31 }}</ref>

<ref name="toshi2009">{{cite press release |url=http://sdd.toshiba.com/techdocs/MKxx33GSG_MK1235GSL_r1.pdf |archive-url=https://web.archive.org/web/20091122075109/http://sdd.toshiba.com/techdocs/MKxx33GSG_MK1235GSL_r1.pdf |archive-date=22 November 2009 |title=Toshiba Introduces Two 1.8-inch Hard Disk Drive Families For Both High Performance and Long Battery Life in Mobile Computing Applications |publisher=Toshiba |date=4 November 2009 |access-date=30 December 2017}}</ref>

<ref name="WDC2005">{{cite web |title=WD Model and Order Numbers |url=http://www.wdc.com/en/library/2579-001028.pdf |archive-url=https://web.archive.org/web/20050824091308/http://www.wdc.com/en/library/2579-001028.pdf |archive-date=2005-08-24 }}</ref>

<ref name="sd-cap-disclaimer">{{cite web |url=http://www.sandisk.com/Assets/Categories/Products/card_capacitydisclaimer.pdf |title=Secure Digital Capacity Disclaimer |work=sandisk.com |publisher=] |access-date=2014-06-20 |archive-url=https://web.archive.org/web/20130227015453/http://www.sandisk.com/Assets/Categories/Products/card_capacitydisclaimer.pdf |archive-date=2013-02-27 }}</ref>

<ref name="msoftxxxx">{{cite web |last=Microsoft |title=Determining Actual Disk Size: Why 1.44&nbsp;MB Should Be 1.40&nbsp;MB |work=Article ID: 121839 |publisher=Microsoft |date=2003-05-06 |url=http://support.microsoft.com/kb/121839 |access-date=2007-07-07}} "The 1.44-megabyte (MB) value associated with the 3.5-inch disk format does not represent the actual size or free space of these disks. Although its size has been popularly called 1.44&nbsp;MB, the correct size is actually 1.40&nbsp;MB."</ref>

<ref name="dvdcap"> {{webarchive |url=https://web.archive.org/web/20110102065839/http://www.osta.org/technology/pdf/dvdqa.pdf#page=20 |date=2 January 2011 }}</ref>

<ref name="cdromcap">{{cite web |url=http://www.videohelp.com/forum/userguides/135642.php |title=Data capacity of CDs |publisher=Videohelp.com |access-date=2012-01-26 |archive-date=2006-07-15 |archive-url=https://web.archive.org/web/20060715075021/http://www.videohelp.com/forum/userguides/135642.php |url-status=dead }}</ref>

<ref name="IBMt2016">{{dead link|date=November 2016 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

<ref name="ECMA2013">{{cite web|url=http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-319.pdf|title=Data Interchange on 12,7 mm 384-Track Magnetic Tape Cartridges – Ultrium-1 Format|website=Ecma-international.org|access-date=30 December 2017|archive-url=https://web.archive.org/web/20130917015428/http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-319.pdf|archive-date=2013-09-17}}</ref>

<ref name="toshi2017">{{cite web|url=http://www.toshiba-tdmt.com.tw/english/products/overview.aspx|title=Client: Client HDD – Toshiba|website=Toshiba-tdmt.com.tw|access-date=30 December 2017|archive-date=2021-04-26 |archive-url=https://web.archive.org/web/20210426174348/http://www.toshiba-tdmt.com.tw/english/products/overview.aspx|url-status=dead}}</ref>

<ref name="IBMaxxxx">{{cite web|url=http://pic.dhe.ibm.com/infocenter/etc/cust/index.jsp?topic=/com.ibm.storage.etc.doc/etc_data_storage_values.html|archive-url=https://archive.today/20140317230133/http://pic.dhe.ibm.com/infocenter/etc/cust/index.jsp?topic=/com.ibm.storage.etc.doc/etc_data_storage_values.html|archive-date=17 March 2014|title=IBM Knowledge Center|website=Pic.dhe.ibm.com|access-date=30 December 2017}}</ref>

<ref name="resp2011">DeRespinis, F., Hayward, P., Jenkins, J., Laird, A., McDonald, L., and Radzinski, E. (2011): ''The IBM style guide: conventions for writers and editors''. IBM Press. quote: "To help avoid inaccuracy (especially with the larger prefixes) and potential ambiguity, the International Electrotechnical Commission (IEC) in 2000 adopted a set of prefixes specifically for binary multipliers (See IEC 60027-2). Their use is now supported by the United States National Institute of Standards and Technology (NIST) and incorporated into ISO 80000. They are also required by EU law and in certain contexts in the US. However, most documentation and products in the industry continue to use SI prefixes when referring to binary multipliers. In product documentation, follow the same standard that is used in the product itself (for example, in the interface or firmware). Whether you choose to use IEC prefixes for powers of 2 and SI prefixes for powers of 10, or use SI prefixes for a dual purpose ... be consistent in your usage and explain to the user your adopted system."</ref>

<ref name="pate2011">{{cite web |title=Patent WO2012098399A2 – Low-power oscillator – Google Patents |website=Google.com |url=https://patents.google.com/patent/WO2012098399A2/en |access-date=2016-06-23}}</ref>

<ref name="ains2022">{{cite journal |title=A terminology standard for underwater acoustics and the benefits of international standardization. |author-last1=Ainslie |author-first1=Michael A. |author-last2=Halvorsen |author-first2=Michele B. |author-last3=Robinson |author-first3=Stephen P. |orig-date=2021-11-09 |date=January 2022 |issn=0364-9059 |eissn=1558-1691 |journal=] |publisher=] |volume=47 |issue=1 |pages=179–200 |doi=10.1109/JOE.2021.3085947 |bibcode=2022IJOE...47..179A |s2cid=243948953 |doi-access=free }} (22 pages)</ref>

}}

== Further reading ==
* {{cite web|url=http://www.iec.ch/zone/si/si_bytes.htm|archive-url=https://web.archive.org/web/20090403051731/http://www.iec.ch/zone/si/si_bytes.htm|archive-date=2009-04-03|title=When is a kilobyte a kibibyte? And an MB an MiB?|publisher=International Electrotechnical Commission|date=2007-02-12}} – An introduction to binary prefixes
* {{cite web|url=http://physics.nist.gov/cuu/Units/binary.html|title=Prefixes for binary multiples|publisher=]}} * {{cite web|url=http://physics.nist.gov/cuu/Units/binary.html|title=Prefixes for binary multiples|publisher=]}}
* {{cite press release|url=http://www.nist.gov/public_affairs/techbeat/tb9903.htm#Information%20Technology|title=Get Ready for the mebi, gibi and tebi|publisher=]|date=]}} * {{Cite press release|url=https://www.nist.gov/public_affairs/techbeat/tb9903.htm#Information%20Technology|title=Get Ready for the mebi, gibi and tebi|publisher=]|date=1999-03-02|access-date=2017-07-13 |archive-date=2016-08-20 |archive-url=https://web.archive.org/web/20160820141603/http://www.nist.gov/public_affairs/techbeat/tb9903.htm#Information%20Technology}}
* {{cite web|url=http://www.cl.cam.ac.uk/~mgk25/information-units.txt|title=What is a Megabyte ...?|author=Markus Kuhn|date=]}}&mdash;a 1996&ndash;1999 paper on bits, bytes, prefixes and symbols * {{cite web|url=http://www.cl.cam.ac.uk/~mgk25/information-units.txt|title=What is a Megabyte ...?|author-first=Markus |author-last=Kuhn|author-link=Markus Kuhn (computer scientist)|date=1996-12-29}}—a 1996–1999 paper on bits, bytes, prefixes and symbols
* {{cite web|url=http://homepages.tesco.net/~J.deBoynePollard/FGA/1mb44-is-not-a-standard-floppy-disc-size.html|author=Jonathan de Boyne Pollard|title=There is no such thing as a 1.44 MB standard format floppy disc}} * {{cite web|url=http://jdebp.eu./FGA/1mb44-is-not-a-standard-floppy-disc-size.html|author-first=Jonathan|author-last=de Boyne Pollard|title=There is no such thing as a 1.44&nbsp;MB standard format floppy disc|work=Frequently Given Answers|archive-url=https://web.archive.org/web/20161007222128/https://jdebp.eu/FGA/1mb44-is-not-a-standard-floppy-disc-size.html|archive-date=2016-10-07}}
* {{cite web|url=http://www.quinion.com/words/turnsofphrase/tp-kib1.htm|title=Kibibyte|date=]|author=Michael Quinion|work=World Wide Words}}&mdash;Another description of binary prefixes * {{cite web|url=http://www.quinion.com/words/turnsofphrase/tp-kib1.htm|title=Kibibyte|date=1999-08-21|author=Michael Quinion|work=World Wide Words|access-date=2002-11-13 |archive-date=2004-06-12 |archive-url=https://web.archive.org/web/20040612044148/http://www.quinion.com/words/turnsofphrase/tp-kib1.htm}}—Another description of binary prefixes
* {{cite paper|format=PDF|url=http://www.wiebetech.com/pressreleases/BillionEqualBillion.pdf|title=When One Billion does not equal One Billion, or: Why your computer's disk drive capacity doesn’t appear to match the stated capacity|author=James Wiebe|date=]}}&mdash;White-paper on the controversy over drive capacities * {{Cite press release |url=http://www.wiebetech.com/pressreleases/BillionEqualBillion.pdf|title=When One Billion does not equal One Billion, or: Why your computer's disk drive capacity doesn't appear to match the stated capacity |website=WiebeTech |author=James Wiebe|date=2003-10-09|access-date=2010-01-22|journal=|archive-date=2013-12-04 |archive-url=https://web.archive.org/web/20131204100206/http://www.wiebetech.com/pressreleases/BillionEqualBillion.pdf}}—White-paper on the controversy over drive capacities


== External links == == External links ==
* *
* ; {{Webarchive|url=https://web.archive.org/web/20150102192754/http://knowledge.seagate.com/articles/en_US/FAQ/002046en?language=en_US |date=2015-01-02 }}
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{{Computer Storage Volumes}}
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Latest revision as of 21:39, 6 January 2025

Symbol placed before units of digital information to indicate multiplication by a power of two This article is about powers-of-two prefixes for measurement units like bit and byte. For notations for the radix of a numeral, see Integer literal § Affixes.

"Gibi" redirects here. For other uses, see Gibi (disambiguation).
Prefixes for decimal and binary multiples
Decimal
Value SI
1000 10 k kilo
1000 10 M mega
1000 10 G giga
1000 10 T tera
1000 10 P peta
1000 10 E exa
1000 10 Z zetta
1000 10 Y yotta
1000 10 R ronna
1000 10 Q quetta
Binary
Value IEC JEDEC
1024 2 Ki kibi K kilo
1024 2 Mi mebi M mega
1024 2 Gi gibi G giga
1024 2 Ti tebi T tera
1024 2 Pi pebi
1024 2 Ei exbi
1024 2 Zi zebi
1024 2 Yi yobi

A binary prefix is a unit prefix that indicates a multiple of a unit of measurement by an integer power of two. The most commonly used binary prefixes are kibi (symbol Ki, meaning 2 = 1024), mebi (Mi, 2 = 1048576), and gibi (Gi, 2 = 1073741824). They are most often used in information technology as multipliers of bit and byte, when expressing the capacity of storage devices or the size of computer files.

The binary prefixes "kibi", "mebi", etc. were defined in 1999 by the International Electrotechnical Commission (IEC), in the IEC 60027-2 standard (Amendment 2). They were meant to replace the metric (SI) decimal power prefixes, such as "kilo" (k, 10 = 1000), "mega" (M, 10 = 1000000) and "giga" (G, 10 = 1000000000), that were commonly used in the computer industry to indicate the nearest powers of two. For example, a memory module whose capacity was specified by the manufacturer as "2 megabytes" or "2 MB" would hold 2 × 2 = 2097152 bytes, instead of 2 × 10 = 2000000.

On the other hand, a hard disk whose capacity is specified by the manufacturer as "10 gigabytes" or "10 GB", holds 10 × 10 = 10000000000 bytes, or a little more than that, but less than 10 × 2 = 10737418240 and a file whose size is listed as "2.3 GB" may have a size closer to 2.3 × 2 ≈ 2470000000 or to 2.3 × 10 = 2300000000, depending on the program or operating system providing that measurement. This kind of ambiguity is often confusing to computer system users and has resulted in lawsuits. The IEC 60027-2 binary prefixes have been incorporated in the ISO/IEC 80000 standard and are supported by other standards bodies, including the BIPM, which defines the SI system, the US NIST, and the European Union.

Prior to the 1999 IEC standard, some industry organizations, such as the Joint Electron Device Engineering Council (JEDEC), attempted to redefine the terms kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB, and GB in the binary sense, for use in storage capacity measurements. However, other computer industry sectors (such as magnetic storage) continued using those same terms and symbols with the decimal meaning. Since then, the major standards organizations have expressly disapproved the use of SI prefixes to denote binary multiples, and recommended or mandated the use of the IEC prefixes for that purpose, but the use of SI prefixes in this sense has persisted in some fields.

Definitions

Specific units of IEC 60027-2 A.2 and ISO/IEC 80000:13-2008
IEC prefix Representations
Name Symbol Base 2 Base 1024 Value Base 10
kibi Ki 2 1024 1024 = 1.024×10
mebi Mi 2 1024 1048576 ≈ 1.049×10
gibi Gi 2 1024 1073741824 ≈ 1.074×10
tebi Ti 2 1024 1099511627776 ≈ 1.100×10
pebi Pi 2 1024 1125899906842624 ≈ 1.126×10
exbi Ei 2 1024 1152921504606846976 ≈ 1.153×10
zebi Zi 2 1024 1180591620717411303424 ≈ 1.181×10
yobi Yi 2 1024 1208925819614629174706176 ≈ 1.209×10

In 2022, the International Bureau of Weights and Measures (BIPM) adopted the decimal prefixes ronna for 1000 and quetta for 1000. In analogy to the existing binary prefixes, a consultation paper of the International Committee for Weights and Measures' Consultative Committee for Units (CCU) suggested the prefixes robi (Ri, 1024) and quebi (Qi, 1024) for their binary counterparts, but as of 2022, no corresponding binary prefixes have been adopted.

Comparison of binary and decimal prefixes

The relative difference between the values in the binary and decimal interpretations increases, when using the SI prefixes as the base, from 2.4% for kilo to nearly 27% for the quetta prefix. Although the prefixes ronna and quetta have been defined, as of 2022 no names have been officially assigned to the corresponding binary prefixes.

Prefix Binary ÷ Decimal Decimal ÷ Binary
kilo kibi 1.024 (+2.4%)   0.9766 (−2.3%)  
mega mebi 1.049 (+4.9%)   0.9537 (−4.6%)  
giga gibi 1.074 (+7.4%)   0.9313 (−6.9%)  
tera tebi 1.100 (+10.0%)   0.9095 (−9.1%)  
peta pebi 1.126 (+12.6%)   0.8882 (−11.2%)  
exa exbi 1.153 (+15.3%)   0.8674 (−13.3%)  
zetta zebi 1.181 (+18.1%)   0.8470 (−15.3%)  
yotta yobi 1.209 (+20.9%)   0.8272 (−17.3%)  
ronna 1.238 (+23.8%)   0.8078 (−19.2%)  
quetta 1.268 (+26.8%)   0.7889 (−21.1%)  

History

See also: Timeline of binary prefixes

Early prefixes

The original metric system adopted by France in 1795 included two binary prefixes named double- (2×) and demi- (⁠1/2⁠×). However, these were not retained when the SI prefixes were internationally adopted by the 11th CGPM conference in 1960.

Storage capacity

Main memory

Early computers used one of two addressing methods to access the system memory; binary (base 2) or decimal (base 10). For example, the IBM 701 (1952) used a binary methods and could address 2048 words of 36 bits each, while the IBM 702 (1953) used a decimal system, and could address ten thousand 7-bit words.

By the mid-1960s, binary addressing had become the standard architecture in most computer designs, and main memory sizes were most commonly powers of two. This is the most natural configuration for memory, as all combinations of states of their address lines map to a valid address, allowing easy aggregation into a larger block of memory with contiguous addresses.

While early documentation specified those memory sizes as exact numbers such as 4096, 8192, or 16384 units (usually words, bytes, or bits), computer professionals also started using the long-established metric system prefixes "kilo", "mega", "giga", etc., defined to be powers of 10, to mean instead the nearest powers of two; namely, 2 = 1024, 2 = 1024, 2 = 1024, etc. The corresponding metric prefix symbols ("k", "M", "G", etc.) were used with the same binary meanings. The symbol for 2 = 1024 could be written either in lower case ("k") or in uppercase ("K"). The latter was often used intentionally to indicate the binary rather than decimal meaning. This convention, which could not be extended to higher powers, was widely used in the documentation of the IBM 360 (1964) and of the IBM System/370 (1972), of the CDC 7600, of the DEC PDP-11/70 (1975) and of the DEC VAX-11/780 (1977).

In other documents, however, the metric prefixes and their symbols were used to denote powers of 10, but usually with the understanding that the values given were approximate, often truncated down. Thus, for example, a 1967 document by Control Data Corporation (CDC) abbreviated "2 = 64 × 1024 = 65536 words" as "65K words" (rather than "64K" or "66K"), while the documentation of the HP 21MX real-time computer (1974) denoted 3 × 2 = 192 × 1024 = 196608 as "196K" and 2 = 1048576 as "1M".

These three possible meanings of "k" and "K" ("1024", "1000", or "approximately 1000") were used loosely around the same time, sometimes by the same company. The HP 3000 business computer (1973) could have "64K", "96K", or "128K" bytes of memory. The use of SI prefixes, and the use of "K" instead of "k" remained popular in computer-related publications well into the 21st century, although the ambiguity persisted. The correct meaning was often clear from the context; for instance, in a binary-addressed computer, the true memory size had to be either a power of 2, or a small integer multiple thereof. Thus a "512 megabyte" RAM module was generally understood to have 512 × 1024 = 536870912 bytes, rather than 512000000.

Hard disks

In specifying disk drive capacities, manufacturers have always used conventional decimal SI prefixes representing powers of 10. Storage in a rotating disk drive is organized in platters and tracks whose sizes and counts are determined by mechanical engineering constraints so that the capacity of a disk drive has hardly ever been a simple multiple of a power of 2. For example, the first commercially sold disk drive, the IBM 350 (1956), had 50 physical disk platters containing a total of 50000 sectors of 100 characters each, for a total quoted capacity of 5 million characters.

Moreover, since the 1960s, many disk drives used IBM's disk format, where each track was divided into blocks of user-specified size; and the block sizes were recorded on the disk, subtracting from the usable capacity. For example, the IBM 3336 disk pack was quoted to have a 200-megabyte capacity, achieved only with a single 13030-byte block in each of its 808 × 19 tracks.

Decimal megabytes were used for disk capacity by the CDC in 1974. The Seagate ST-412, one of several types installed in the IBM PC/XT, had a capacity of 10027008 bytes when formatted as 306 × 4 tracks and 32 256-byte sectors per track, which was quoted as "10 MB". Similarly, a "300 GB" hard drive can be expected to offer only slightly more than 300×10 = 300000000000, bytes, not 300 × 2 (which would be about 322×10 bytes or "322 GB"). The first terabyte (SI prefix, 1000000000000 bytes) hard disk drive was introduced in 2007. Decimal prefixes were generally used by information processing publications when comparing hard disk capacities.

Some programs and operating systems, such as Microsoft Windows, still use "MB" and "GB" to denote binary prefixes even when displaying disk drive capacities and file sizes, as did Classic Mac OS. Thus, for example, the capacity of a "10 MB" (decimal "M") disk drive could be reported as "9.56 MB", and that of a "300 GB" drive as "279.4 GB". Some operating systems, such as Mac OS X, Ubuntu, and Debian, have been updated to use "MB" and "GB" to denote decimal prefixes when displaying disk drive capacities and file sizes. Some manufacturers, such as Seagate Technology, have released recommendations stating that properly-written software and documentation should specify clearly whether prefixes such as "K", "M", or "G" mean binary or decimal multipliers.

Floppy disks

Floppy disks used a variety of formats, and their capacities was usually specified with SI-like prefixes "K" and "M" with either decimal or binary meaning. The capacity of the disks was often specified without accounting for the internal formatting overhead, leading to more irregularities.

The early 8-inch diskette formats could contain less than a megabyte with the capacities of those devices specified in kilobytes, kilobits or megabits.

The 5.25-inch diskette sold with the IBM PC AT could hold 1200 × 1024 = 1228800 bytes, and thus was marketed as "1200 KB" with the binary sense of "KB". However, the capacity was also quoted "1.2 MB", which was a hybrid decimal and binary notation, since the "M" meant 1000 × 1024. The precise value was 1.2288 MB (decimal) or 1.171875 MiB (binary).

The 5.25-inch Apple Disk II had 256 bytes per sector, 13 sectors per track, 35 tracks per side, or a total capacity of 116480 bytes. It was later upgraded to 16 sectors per track, giving a total of 140 × 2 = 143360 bytes, which was described as "140KB" using the binary sense of "K".

The most recent version of the physical hardware, the "3.5-inch diskette" cartridge, had 720 512-byte blocks (single-sided). Since two blocks comprised 1024 bytes, the capacity was quoted "360 KB", with the binary sense of "K". On the other hand, the quoted capacity of "1.44 MB" of the High Density ("HD") version was again a hybrid decimal and binary notation, since it meant 1440 pairs of 512-byte sectors, or 1440 × 2 = 1474560 bytes. Some operating systems displayed the capacity of those disks using the binary sense of "MB", as "1.4 MB" (which would be 1.4 × 2 ≈ 1468000 bytes). User complaints forced both Apple and Microsoft to issue support bulletins explaining the discrepancy.

Optical disks

When specifying the capacities of optical compact discs, "megabyte" and "MB" usually meant 1024 bytes. Thus a "700-MB" (or "80-minute") CD has a nominal capacity of about 700 MiB, which is approximately 730 MB (decimal).

On the other hand, capacities of other optical disc storage media like DVD, Blu-ray Disc, HD DVD and magneto-optical (MO) have been generally specified in decimal gigabytes ("GB"), that is, 1000 bytes. In particular, a typical "4.7 GB" DVD has a nominal capacity of about 4.7×10 bytes, which is about 4.38 GiB.

Tape drives and media

Tape drive and media manufacturers have generally used SI decimal prefixes to specify the maximum capacity, although the actual capacity would depend on the block size used when recording.

Data and clock rates

Computer clock frequencies are always quoted using SI prefixes in their decimal sense. For example, the internal clock frequency of the original IBM PC was 4.77 MHz, that is 4770000 Hz.

Similarly, digital information transfer rates are quoted using decimal prefixe. The Parallel ATA "100 MB/s" disk interface can transfer 100000000 bytes per second, and a "56 Kb/s" modem transmits 56000 bits per second. Seagate specified the sustained transfer rate of some hard disk drive models with both decimal and IEC binary prefixes. The standard sampling rate of music compact disks, quoted as 44.1 kHz, is indeed 44100 samples per second. A "1 Gb/s" Ethernet interface can receive or transmit up to 10 bits per second, or 125000000 bytes per second within each packet. A "56k" modem can encode or decode up to 56000 bits per second.

Decimal SI prefixes are also generally used for processor-memory data transfer speeds. A PCI-X bus with 66 MHz clock and 64 bits wide can transfer 66000000 64-bit words per second, or 4224000000 bit/s = 528000000 B/s, which is usually quoted as 528 MB/s. A PC3200 memory on a double data rate bus, transferring 8 bytes per cycle with a clock speed of 200 MHz has a bandwidth of 200000000 × 8 × 2 = 3200000000 B/s, which would be quoted as 3.2 GB/s.

Ambiguous standards

The ambiguous usage of the prefixes "kilo ("K" or "k"), "mega" ("M"), and "giga" ("G"), as meaning both powers of 1000 or (in computer contexts) of 1024, has been recorded in popular dictionaries, and even in some obsolete standards, such as ANSI/IEEE 1084-1986 and ANSI/IEEE 1212-1991, IEEE 610.10-1994, and IEEE 100-2000. Some of these standards specifically limited the binary meaning to multiples of "byte" ("B") or "bit" ("b").

Early binary prefix proposals

Before the IEC standard, several alternative proposals existed for unique binary prefixes, starting in the late 1960s. In 1996, Markus Kuhn proposed the extra prefix "di" and the symbol suffix or subscript "2" to mean "binary"; so that, for example, "one dikilobyte" would mean "1024 bytes", denoted "K2B" or "K2B".

In 1968, Donald Morrison proposed to use the Greek letter kappa (κ) to denote 1024, κ to denote 1024, and so on. (At the time, memory size was small, and only K was in widespread use.) In the same year, Wallace Givens responded with a suggestion to use bK as an abbreviation for 1024 and bK2 or bK for 1024, though he noted that neither the Greek letter nor lowercase letter b would be easy to reproduce on computer printers of the day. Bruce Alan Martin of Brookhaven National Laboratory proposed that, instead of prefixes, binary powers of two were indicated by the letter B followed by the exponent, similar to E in decimal scientific notation. Thus one would write 3B20 for 3 × 2. This convention is still used on some calculators to present binary floating point-numbers today.

In 1969, Donald Knuth, who uses decimal notation like 1 MB = 1000 kB, proposed that the powers of 1024 be designated as "large kilobytes" and "large megabytes", with abbreviations KKB and MMB.

Consumer confusion

The ambiguous meanings of "kilo", "mega", "giga", etc., has caused significant consumer confusion, especially in the personal computer era. A common source of confusion was the discrepancy between the capacities of hard drives specified by manufacturers, using those prefixes in the decimal sense, and the numbers reported by operating systems and other software, that used them in the binary sense, such as the Apple Macintosh in 1984. For example, a hard drive marketed as "1 TB" could be reported as having only "931 GB". The confusion was compounded by fact that RAM manufacturers used the binary sense too.

Legal disputes

The different interpretations of disk size prefixes led to class action lawsuits against digital storage manufacturers. These cases involved both flash memory and hard disk drives.

Early cases

Early cases (2004–2007) were settled prior to any court ruling with the manufacturers admitting no wrongdoing but agreeing to clarify the storage capacity of their products on the consumer packaging. Accordingly, many flash memory and hard disk manufacturers have disclosures on their packaging and web sites clarifying the formatted capacity of the devices or defining MB as 1 million bytes and 1 GB as 1 billion bytes.

Willem Vroegh v. Eastman Kodak Company

On 20 February 2004, Willem Vroegh filed a lawsuit against Lexar Media, Dane–Elec Memory, Fuji Photo Film USA, Eastman Kodak Company, Kingston Technology Company, Inc., Memorex Products, Inc.; PNY Technologies Inc., SanDisk Corporation, Verbatim Corporation, and Viking Interworks alleging that their descriptions of the capacity of their flash memory cards were false and misleading.

Vroegh claimed that a 256 MB Flash Memory Device had only 244 MB of accessible memory. "Plaintiffs allege that Defendants marketed the memory capacity of their products by assuming that one megabyte equals one million bytes and one gigabyte equals one billion bytes." The plaintiffs wanted the defendants to use the customary values of 1024 for megabyte and 1024 for gigabyte. The plaintiffs acknowledged that the IEC and IEEE standards define a MB as one million bytes but stated that the industry has largely ignored the IEC standards.

The parties agreed that manufacturers could continue to use the decimal definition so long as the definition was added to the packaging and web sites. The consumers could apply for "a discount of ten percent off a future online purchase from Defendants' Online Stores Flash Memory Device".

Orin Safier v. Western Digital Corporation

On 7 July 2005, an action entitled Orin Safier v. Western Digital Corporation, et al. was filed in the Superior Court for the City and County of San Francisco, Case No. CGC-05-442812. The case was subsequently moved to the Northern District of California, Case No. 05-03353 BZ.

Although Western Digital maintained that their usage of units is consistent with "the indisputably correct industry standard for measuring and describing storage capacity", and that they "cannot be expected to reform the software industry", they agreed to settle in March 2006 with 14 June 2006 as the Final Approval hearing date.

Western Digital offered to compensate customers with a gratis download of backup and recovery software that they valued at US$30. They also paid $500000 in fees and expenses to San Francisco lawyers Adam Gutride and Seth Safier, who filed the suit. The settlement called for Western Digital to add a disclaimer to their later packaging and advertising. Western Digital had this footnote in their settlement. "Apparently, Plaintiff believes that he could sue an egg company for fraud for labeling a carton of 12 eggs a 'dozen', because some bakers would view a 'dozen' as including 13 items."

Cho v. Seagate Technology (US) Holdings, Inc.

A lawsuit (Cho v. Seagate Technology (US) Holdings, Inc., San Francisco Superior Court, Case No. CGC-06-453195) was filed against Seagate Technology, alleging that Seagate overrepresented the amount of usable storage by 7% on hard drives sold between 22 March 2001 and 26 September 2007. The case was settled without Seagate admitting wrongdoing, but agreeing to supply those purchasers with gratis backup software or a 5% refund on the cost of the drives.

Dinan et al. v. SanDisk LLC

On 22 January 2020, the district court of the Northern District of California ruled in favor of the defendant, SanDisk, upholding its use of "GB" to mean 1000000000 bytes.

IEC 1999 Standard

In 1995, the International Union of Pure and Applied Chemistry's (IUPAC) Interdivisional Committee on Nomenclature and Symbols (IDCNS) proposed the prefixes "kibi" (short for "kilobinary"), "mebi" ("megabinary"), "gibi" ("gigabinary") and "tebi" ("terabinary"), with respective symbols "kb", "Mb", "Gb" and "Tb", for binary multipliers. The proposal suggested that the SI prefixes should be used only for powers of 10; so that a disk drive capacity of "500 gigabytes", "0.5 terabytes", "500 GB", or "0.5 TB" should all mean 500×10 bytes, exactly or approximately, rather than 500 × 2 (= 536870912000) or 0.5 × 2 (= 549755813888).

The proposal was not accepted by IUPAC at the time, but was taken up in 1996 by the Institute of Electrical and Electronics Engineers (IEEE) in collaboration with the International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC). The prefixes "kibi", "mebi", "gibi" and "tebi" were retained, but with the symbols "Ki" (with capital "K"), "Mi", "Gi" and "Ti" respectively.

In January 1999, the IEC published this proposal, with additional prefixes "pebi" ("Pi") and "exbi" ("Ei"), as an international standard (IEC 60027-2 Amendment 2) The standard reaffirmed the BIPM's position that the SI prefixes should always denote powers of 10. The third edition of the standard, published in 2005, added prefixes "zebi" and "yobi", thus matching all then-defined SI prefixes with binary counterparts.

The harmonized ISO/IEC IEC 80000-13:2008 standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005 (those defining prefixes for binary multiples). The only significant change is the addition of explicit definitions for some quantities. In 2009, the prefixes kibi-, mebi-, etc. were defined by ISO 80000-1 in their own right, independently of the kibibyte, mebibyte, and so on.

The BIPM standard JCGM 200:2012 "International vocabulary of metrology – Basic and general concepts and associated terms (VIM), 3rd edition" lists the IEC binary prefixes and states "SI prefixes refer strictly to powers of 10, and should not be used for powers of 2. For example, 1 kilobit should not be used to represent 1024 bits (2 bits), which is 1 kibibit."

The IEC 60027-2 standard recommended operating systems and other software were updated to use binary or decimal prefixes consistently, but incorrect usage of SI prefixes for binary multiples is still common. At the time, the IEEE decided that their standards would use the prefixes "kilo", etc. with their metric definitions, but allowed the binary definitions to be used in an interim period as long as such usage was explicitly pointed out on a case-by-case basis.

Other standards bodies and organizations

The IEC standard binary prefixes are supported by other standardization bodies and technical organizations.

The United States National Institute of Standards and Technology (NIST) supports the ISO/IEC standards for "Prefixes for binary multiples" and has a web page documenting them, describing and justifying their use. NIST suggests that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced as bee. NIST has stated the SI prefixes "refer strictly to powers of 10" and that the binary definitions "should not be used" for them.

As of 2014, the microelectronics industry standards body JEDEC describes the IEC prefixes in its online dictionary, but acknowledges that the SI prefixes and the symbols "K", "M" and "G" are still commonly used with the binary sense for memory sizes.

On 19 March 2005, the IEEE standard IEEE 1541-2002 ("Prefixes for Binary Multiples") was elevated to a full-use standard by the IEEE Standards Association after a two-year trial period. as of April 2008, the IEEE Publications division does not require the use of IEC prefixes in its major magazines such as Spectrum or Computer.

The International Bureau of Weights and Measures (BIPM), which maintains the International System of Units (SI), expressly prohibits the use of SI prefixes to denote binary multiples, and recommends the use of the IEC prefixes as an alternative since units of information are not included in the SI.

The Society of Automotive Engineers (SAE) prohibits the use of SI prefixes with anything but a power-of-1000 meaning, but does not cite the IEC binary prefixes.

The European Committee for Electrotechnical Standardization (CENELEC) adopted the IEC-recommended binary prefixes via the harmonization document HD 60027-2:2003-03. The European Union (EU) has required the use of the IEC binary prefixes since 2007.

Current practice

The 536870912-byte capacity of these RAM modules is stated as "512 MB" on the label.
GNOME's partition editor uses IEC prefixes to display partition sizes. The total capacity of the 120 × 10-byte disk is displayed as "111.79 GiB".
GNOME's system monitor uses IEC prefixes to show memory size and networking data rate.

Some computer industry participants, such as Hewlett-Packard (HP), and IBM have adopted or recommended IEC binary prefixes as part of their general documentation policies.

As of 2023, the use of SI prefixes with the binary meanings is still prevalent for specifying the capacity of the main memory of computers, of RAM, ROM, EPROM, and EEPROM chips and memory modules, and of the cache of computer processors. For example, a "512-megabyte" or "512 MB" memory module holds 512 MiB; that is, 512 × 2 bytes, not 512 × 10 bytes.

JEDEC continues to include the customary binary definitions of "kilo", "mega", and "giga" in the document Terms, Definitions, and Letter Symbols, and, as of 2010, still used those definitions in their memory standards.

On the other hand, the SI prefixes with powers of ten meanings are generally used for the capacity of external storage units, such as disk drives, solid state drives, and USB flash drives, except for some flash memory chips intended to be used as EEPROMs. However, some disk manufacturers have used the IEC prefixes to avoid confusion. The decimal meaning of SI prefixes is usually also intended in measurements of data transfer rates, and clock speeds.

Some operating systems and other software use either the IEC binary multiplier symbols ("Ki", "Mi", etc.) or the SI multiplier symbols ("k", "M", "G", etc.) with decimal meaning. Some programs, such as the GNU ls command, let the user choose between binary or decimal multipliers. However, some continue to use the SI symbols with the binary meanings, even when reporting disk or file sizes. Some programs may also use "K" instead of "k", with either meaning.

Other uses

While the binary prefixes are almost always used with the units of information, bits and bytes, they may be used with any other unit of measure, when convenient. For example, in signal processing one may need binary multiples of the frequency unit hertz (Hz), for example the kibihertz (KiHz), equal to 1024 Hz.

See also

References

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Further reading

External links

Units of information
Platform-independent units
Platform-dependent units
Metric bit units
Metric byte units
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