Author: Robert Hyatt
Date: 20:11:22 03/09/00
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On March 09, 2000 at 22:28:33, Tom Kerrigan wrote: >On March 09, 2000 at 22:18:12, Eugene Nalimov wrote: > >>Is 8080 16-bit processor? It has 3 register pairs, each 16-bit wise, and there >>were operations that worked at those - addition, load, store. And z80 adds more >>16-bit instructions - e.g subtraction with carry. >> >>On 68000 32-bit operations worked much slower than 16-bit operations, even for >>data on registers. >> >>Eugene > >How wide was the register bus in the 8080? My guess is 8 bits. I believe the >register bus in the 68000 was 32. I don't think instruction speed has a place in >determining the "bitiness" of a processor. > >-Tom I think the easy test is that every N bit processor I have ever used also had some 2*N bit instructions. IE when you do a multiply or divide, you have to do that or take a big integer precision hit. My old xerox sigma9 was 32 bit, but you could use several instructions that would take an even-odd register pair and treat them as one. Ditto for the old 32 bit vax. Older PDP-11's had 16 bit everything, but had some 32 bit instructions as above... Simple test is "what did Motorola call this microprocessor?" 16 bit or 32 bit? I want to say "16 bit" but I used them so long ago I am not certain. Last time I touched one was 1985 before I left USM and stopped teaching hardware design courses... as a result, I don't have any of the motorola poop sheets handy...
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