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| {{Redirect|CMOS RAM|other types of CMOS RAM|Random-access memory}} | {{Redirect|CMOS RAM|other types of CMOS RAM|Random-access memory}} | ||
| {{Cleanup rewrite|date=May 2021}} | {{Cleanup rewrite|date=May 2021}} | ||
| ] | ] | ||
| ] motherboard]] | ] motherboard]] | ||
| '''Nonvolatile BIOS memory''' refers to a small ] on ] ]s that is used to store ] settings. It is traditionally called '''CMOS''' RAM because it uses a ], low-power ] ] (such as the ] MC146818 or similar) powered by a small |
'''Nonvolatile BIOS memory''' refers to a small ] on ] ]s that is used to store ] settings. It is traditionally called '''CMOS''' RAM because it uses a ], low-power ] ] (such as the ] MC146818<ref>{{cite book | url=https://books.google.com/books?id=E1p2FDL7P5QC&dq=bios+cmos&pg=PA393 | title=Upgrading and Repairing PCS | isbn=978-0-7897-2974-3 | last1=Mueller | first1=Scott | date=2004 | publisher=Que }}</ref> or similar) powered by a small battery when system and standby power is off.<ref name=whatiscmos>{{cite web |url=http://pcsupport.about.com/od/termsc/g/cmos.htm |title=What is CMOS? (CMOS & CMOS Battery Definition) |publisher=] |first=Tim |last=Fisher |access-date=2 September 2015 |archive-date=9 August 2016 |archive-url=https://web.archive.org/web/20160809082556/http://pcsupport.about.com/od/termsc/g/cmos.htm |url-status=dead }}</ref> It is referred to as non-volatile memory or ] because, after the system loses power, it does retain state by virtue of the CMOS battery. When the battery fails, BIOS settings are reset to their defaults. The battery can also be used to power a real time clock (RTC) and the RTC, NVRAM and battery may be integrated into a single component. The name CMOS memory comes from the technology used to make the memory, which is easier to say than NVRAM.<ref>{{cite book | url=https://books.google.com/books?id=eV1_LjW3pTkC&dq=cmos+bios+settings+only+one+with+cmos&pg=PA382 | title=Upgrading and Repairing PCS | isbn=978-0-7897-2745-9 | last1=Mueller | first1=Scott | date=2003 | publisher=Que }}</ref> | ||
| The CMOS RAM and the real-time clock have been integrated as a part of the ] chipset and |
The CMOS RAM and the real-time clock have been integrated as a part of the ] chipset and they may not be standalone chips on modern motherboards.<ref name="100Series">{{cite web|url=http://www.intel.com/content/www/us/en/chipsets/100-series-chipset-datasheet-vol-1.html |title=Intel 100 Series Chipset Family PCH Datasheet| publisher=Intel |date=August 2015 |access-date=16 April 2016}}</ref><ref>{{cite web|url=https://www.intel.com/Assets/PDF/datasheet/290562.pdf|title=82430FX PCISET Data Sheet|publisher=Intel|access-date=23 January 2023}}</ref> In turn, the southbridge has been integrated into a single ]. Alternatively BIOS settings may be stored in the computer's ] chip.<ref>{{cite book | url=https://books.google.com/books?id=E1p2FDL7P5QC&dq=bios+cmos&pg=PA393 | title=Upgrading and Repairing PCS | isbn=978-0-7897-2974-3 | last1=Mueller | first1=Scott | date=2004 | publisher=Que }}</ref> | ||
| The chipset built-in NVRAM capacity is typically 256 ]s.<ref name="100Series" /> For this reason, later BIOS implementations may use a small portion of BIOS flash ROM as NVRAM, to store setup data.<ref>http://rom.by/files/AMIBIOS8-Flash-Recovery-Whitepaper.pdf {{Bare URL PDF|date=August 2024}}</ref> | |||
| ⚫ | Today's ] motherboards use ] to store configuration data (NVRAM is a |
||
| ⚫ | Today's ] motherboards use ] to store configuration data (NVRAM is a portion of the UEFI ] ROM), but by many ]s' design, the UEFI settings are still lost if the CMOS battery fails.<ref>{{Cite web|title=UEFI NVRAM - OSDev Wiki|url=https://wiki.osdev.org/UEFI_NVRAM|access-date=2020-09-11|website=wiki.osdev.org|df=dmy-all}}</ref><ref>{{Cite book|chapter-url=https://media.springernature.com/original/springer-static/image/chp%3A10.1007%2F978-1-4842-6106-4_4/MediaObjects/488723_1_En_4_Fig6_HTML.png|doi = 10.1007/978-1-4842-6106-4_4|chapter = Firmware Resiliency: Detection|title = Building Secure Firmware|year = 2020|last1 = Yao|first1 = Jiewen|last2 = Zimmer|first2 = Vincent|pages = 115–162|isbn = 978-1-4842-6105-7| s2cid=242541772 }}</ref> | ||
| ==CMOS battery== | |||
| <!-- ] redirects to this section; if this section is renamed, please change the incoming redirect. Thanks! --> | |||
| =={{anchor|Rechargeable CMOS battery}}CMOS battery== | |||
| ], the most common CMOS battery.]] | |||
| {{multiple image|direction=horizontal|image1=Battery-lithium-cr2032.jpg|caption1=] button cell, the most common CMOS battery|image2=NiCd VARTA battery leakage on circuit board (IMG 3313).jpg|caption2=]-manufactured ] barrel battery that has leaked onto the mainboard of a ] and damaged legs and traces|total_width=440}} | |||
| The memory battery (aka motherboard, CMOS, ] (RTC), clock battery)<ref name=whatiscmos /><ref></ref> is generally |
The memory battery (aka motherboard, CMOS, ] (RTC), clock battery)<ref name=whatiscmos /><ref></ref> is generally a ] ] ]. This cell battery has an estimated life of three years when ] is unplugged or when the PSU power switch is turned off.<ref> | ||
| {{ | {{ | ||
| cite web| | cite web| | ||
| Line 21: | Line 22: | ||
| |date=24 August 2020 |publisher=Intel | |date=24 August 2020 |publisher=Intel | ||
| }} | }} | ||
| </ref> This battery type, unlike the ], is not rechargeable and trying to do so may result in an explosion. Motherboards have circuitry preventing batteries from being charged and discharged when a motherboard is powered on. Other common battery cell types can last significantly longer or shorter periods, such as the smaller ] which will generally last about 40% less time than CR2032. Higher temperatures and longer power-off time will shorten battery cell life. When replacing the battery cell, the system time and CMOS ] settings may revert to default values. Unwanted BIOS reset may be avoided by replacing the battery cell with the PSU power switch turned on and plugged into ]. On ] motherboards, the PSU will supply 5V standby power to the motherboard to keep CMOS memory energized while the system is off. | </ref> This battery type, unlike the ], is not rechargeable and trying to do so may result in an explosion. Motherboards have circuitry preventing batteries from being charged and discharged when a motherboard is powered on. Other common battery cell types can last significantly longer or shorter periods, such as the smaller ] which will generally last about 40% less time than CR2032. Higher temperatures and longer power-off time will shorten battery cell life. When replacing the battery cell, the system time and CMOS ] settings may revert to default values. Unwanted BIOS reset may be avoided by replacing the battery cell with the PSU power switch turned on and plugged into ]. On ] motherboards, the PSU will supply 5V standby power to the motherboard to keep CMOS memory energized while the system is off. | ||
| Some computer designs have used non-button cell batteries, such as the cylindrical "]" used in the ] as well as some older ]s, or a 3-cell |
Some computer designs have used non-button cell batteries, such as the cylindrical "]" used in the ] as well as some older ]s, or a 3-cell ] (Ni–Cd) CMOS battery that looks like a "]" (common in ] and older IBM PC compatibles), which serves the same purpose. These motherboards often have a four pin straight header, with pin 2 missing, for connecting to an external 3.6v battery, such as the Tadiran TL-5242/W, when their soldered-on batteries run out. Ni–Cd batteries have a tendency to ] after a period of disuse, damaging components and traces on the circuit board near the battery.<ref>{{cite web | last=Williams | first=Al | date=July 8, 2018 | url=https://hackaday.com/2018/07/08/amiga-2000-emergency-repair/ | title=Amiga 2000 Emergency Repair | work=Hackaday | archiveurl=https://web.archive.org/web/20180708201017/https://hackaday.com/2018/07/08/amiga-2000-emergency-repair/ | archivedate=July 8, 2018}}</ref> | ||
| ==See also== | ==See also== | ||
| * ] | |||
| * ] (ESCD) | * ] (ESCD) | ||
| * ] | |||
| * ] | * ] | ||
| Line 35: | Line 34: | ||
| ==External links== | ==External links== | ||
| * | * | ||
| * | * | ||
| * | |||
| * (video). | * (video). | ||
| * | * | ||
| * | * | ||
| ] | ] | ||
Latest revision as of 03:11, 28 August 2024
Small, battery-backed memory component for storing a computer's BIOS settings "CMOS memory" redirects here. For other types of CMOS memory, see Semiconductor memory. "CMOS RAM" redirects here. For other types of CMOS RAM, see Random-access memory. | This article may need to be rewritten to comply with Misplaced Pages's quality standards. You can help. The talk page may contain suggestions. (May 2021) |
Nonvolatile BIOS memory refers to a small memory on PC motherboards that is used to store BIOS settings. It is traditionally called CMOS RAM because it uses a volatile, low-power complementary metal–oxide–semiconductor (CMOS) SRAM (such as the Motorola MC146818 or similar) powered by a small battery when system and standby power is off. It is referred to as non-volatile memory or NVRAM because, after the system loses power, it does retain state by virtue of the CMOS battery. When the battery fails, BIOS settings are reset to their defaults. The battery can also be used to power a real time clock (RTC) and the RTC, NVRAM and battery may be integrated into a single component. The name CMOS memory comes from the technology used to make the memory, which is easier to say than NVRAM.
The CMOS RAM and the real-time clock have been integrated as a part of the southbridge chipset and they may not be standalone chips on modern motherboards. In turn, the southbridge has been integrated into a single Platform Controller Hub. Alternatively BIOS settings may be stored in the computer's Super I/O chip.
The chipset built-in NVRAM capacity is typically 256 bytes. For this reason, later BIOS implementations may use a small portion of BIOS flash ROM as NVRAM, to store setup data.
Today's UEFI motherboards use NVRAM to store configuration data (NVRAM is a portion of the UEFI flash ROM), but by many OEMs' design, the UEFI settings are still lost if the CMOS battery fails.
CMOS battery
CR-2032 button cell, the most common CMOS battery.jpg)
VARTA-manufactured Ni–Cd barrel battery that has leaked onto the mainboard of a synthesizer and damaged legs and traces
The memory battery (aka motherboard, CMOS, real-time clock (RTC), clock battery) is generally a CR2032 lithium coin cell. This cell battery has an estimated life of three years when power supply unit (PSU) is unplugged or when the PSU power switch is turned off. This battery type, unlike the lithium-ion battery, is not rechargeable and trying to do so may result in an explosion. Motherboards have circuitry preventing batteries from being charged and discharged when a motherboard is powered on. Other common battery cell types can last significantly longer or shorter periods, such as the smaller CR2016 which will generally last about 40% less time than CR2032. Higher temperatures and longer power-off time will shorten battery cell life. When replacing the battery cell, the system time and CMOS BIOS settings may revert to default values. Unwanted BIOS reset may be avoided by replacing the battery cell with the PSU power switch turned on and plugged into an electric wall socket. On ATX motherboards, the PSU will supply 5V standby power to the motherboard to keep CMOS memory energized while the system is off.
Some computer designs have used non-button cell batteries, such as the cylindrical "1/2 AA" used in the Power Mac G4 as well as some older IBM PC compatibles, or a 3-cell nickel–cadmium (Ni–Cd) CMOS battery that looks like a "barrel" (common in Amiga and older IBM PC compatibles), which serves the same purpose. These motherboards often have a four pin straight header, with pin 2 missing, for connecting to an external 3.6v battery, such as the Tadiran TL-5242/W, when their soldered-on batteries run out. Ni–Cd batteries have a tendency to leak devastatingly after a period of disuse, damaging components and traces on the circuit board near the battery.
See also
References
- Mueller, Scott (2004). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2974-3.
- ^ Fisher, Tim. "What is CMOS? (CMOS & CMOS Battery Definition)". About.com. Archived from the original on 9 August 2016. Retrieved 2 September 2015.
- Mueller, Scott (2003). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2745-9.
- ^ "Intel 100 Series Chipset Family PCH Datasheet". Intel. August 2015. Retrieved 16 April 2016.
- "82430FX PCISET Data Sheet" (PDF). Intel. Retrieved 23 January 2023.
- Mueller, Scott (2004). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2974-3.
- http://rom.by/files/AMIBIOS8-Flash-Recovery-Whitepaper.pdf
- "UEFI NVRAM - OSDev Wiki". wiki.osdev.org. Retrieved 11 September 2020.
- Yao, Jiewen; Zimmer, Vincent (2020). "Firmware Resiliency: Detection". Building Secure Firmware. pp. 115–162. doi:10.1007/978-1-4842-6106-4_4. ISBN 978-1-4842-6105-7. S2CID 242541772.
- Ask a question » Replacing the battery of your motherboard (CMOS battery)
- "CMOS Battery on the Intel NUC". Intel. 24 August 2020.
- Williams, Al (July 8, 2018). "Amiga 2000 Emergency Repair". Hackaday. Archived from the original on July 8, 2018.
External links
- Definition of CMOS & CMOS Batteries
- CMOS memory map (for Bochs PC emulator)
- How to replace dead CMOS battery and configure BIOS settings (video).
- Tutorial: How to replace the CMOS battery in your laptop
- How to replace the CMOS battery