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| In ] terminology, '''word size''' ('''word length''') is the number of ]s that a ] can process at one time (the ]). Processors with many different word sizes have existed, where the word size was selected as a trade off between precision and range of numeric results and the cost of the processing hardware. A 12-bit data word was used by some ]s such as the ] ] and is still used on special-purpose ]s such as ]s and ]s. Some early ] systems used 35, ], 40, 44 or 45-bit words, or words that contained between 6 and 16 decimal digits. Word lengths in powers of two (8, 16, 32, 64) have predominated for many years, roughly since the introducionn of the ] System 360. See ], ], ], ], ]. | |||
| A processor's word size for arithmetic is often equal to the width of its external ] though sometimes the bus is made narrower than the CPU (often half as many bits) to economise on packaging and ] costs, space, and power consumption. For machines of the ] type, a word size equal or greater than the logical address size is convenient, though the physical address range of a processor may be greater or less than the word size for arithmetic. | |||
| A word ''n'' bits long can hold 2<sup>''n''</sup> distinct values. If these values represent integers, by far the most common ranges are −2<sup>''n''−1</sup> to 2<sup>''n''−1</sup>−1 inclusive, or 0 to 2<sup>''n''</sup>−1 inclusive. | |||
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| ==Reference== | |||
| Anthony Ralston and Edwin D. Reilly, ''Encyclopedia of Computer Science Third Edition'', Van Nostrand Reinhold, New York, 1993 ISBN 0442276795 | |||
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