seanf@sco.COM (Sean Fagan) (03/06/89)
In article <5988@bsu-cs.UUCP> pervect@bsu-cs.UUCP (Barrett Kreiner) writes: >All machines have an internal WORD size (WORD is *NOT* interchangeable with >BYTE) a BYTE is defined as 8 bits.. a Nybble (havn't used that in a while) is >4 bits. a WORD (on most of all current machines) is a combination of bytes >and bits. now repeat after me.. >WORD != BYTE Very good. You've got that down. >BYTE= 8 bits Then, you blow it here. Byte is a term that, on microprocessors, meant 8 bits. Machines from Unisys's predecessor (I'm showing my age, am't I?) had 9-bit bytes, and 18-bit words. So did quite a few DEC machines. In fact, the PDP-11 and VAX are, I believe, DEC's only machines with 8-bit bytes (if I'm wrong, I'm sure thousands of people will inform me). IBM had 8-bit bytes for their 360, but not necessarily for earlier machines. CDC had 12-bit bytes for the 6600 (that was what the PP's could address), but tended to work with 6-bit bytes, since they could put 10 characters (6-bits each) in a word (60-bits, of course). When they came up with the CMU (Character Move Unit), they had 6-bit bytes. The ARM (Acorn RISC Machine) doesn't really have bytes; everything is word-addressable on it (32-bit words). I could therefore make a case of it having a 32-bit byte. I could go on, through about 30-40 years of computer history, but I think you get the idea. Please not the followup, ok? >bit = binary decimal (0 or 1) This is true. >Nybble = 4 bits = 1/2 byte Nybble is not used always. You could ask a lot of programmers, and they wouldn't know what it is. Usually used by people who use microcomputers. >WORD= anything a manufacuterer feels like.. The definitions that are usually used are: Word = Most comfortable size for ALU et al. For example, a 68000 has a 16-bit word, while a 68020 has a 32-bit word. Byte = Smallest addressable unit. Again, this is not always the case. When it isn't, it's usually used to mean the size of a character (which can be anywhere from 6 to 64 bits!). Sean. -- Sean Eric Fagan | "What the caterpillar calls the end of the world, seanf@sco.UUCP | the master calls a butterfly." -- Richard Bach (408) 458-1422 | Any opinions expressed are my own, not my employers'.