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Word (Computer Science)A word is the amount of computer memory referenced by a single memory address. Large computers have tended historically to have large word sizes. Early IBM mainframes might have a 60-bit word; MULTICS and TWENEX systems both used 36-bit words with a 9-bit byte; the VAX had a 32-bit word. The advantage of a large word size is two-fold. Firstly, it makes the amount of memory held in a single address larger, so the same size address space holds more actual memory. Secondly, greater word length allows a greater address space, as addresses are typically held in a fixed number of words. However, there is a certain ambiguity in the notion of a word. A system might be able to address individual bytes but have a processor capable of loading a 32-bit integer and operating on it at once; is such a system using an eight-bit, or a thirty-two bit word? The Atari ST could address individual bytes, had a 16-bit data bus, meaning it could only load 16 bits at any one time, and a 32-bit register size, meaning it could carry out 32-bit operations. It was generally regarded as a 16-bit microcomputer. Neither its minimal address size nor its register size were 16-bit, so it is possible we must enter yet a third definition of word, relating to the data bus size. Any clarification on this issue can only be of assistance to the community at large. See word.
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