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1. Julia Evans (b0rk@social.jvns.ca)'s status on Tuesday, 07-Mar-2023 02:07:47 JST Julia Evans

   everyone keeps asking me why x86 uses an 8-bit byte, but I'm struggling to find an explanation that makes sense to me. Can any of you help?

   what I've found so far
   - it looks like x86 evolved from the intel 8008 (from 1972), which was an 8-bit CPU
   - the 8008 came after the 4004, which was 4-bit

   some questions I have:
   - was the reason to build an 8-bit CPU to increase the size of the instruction set? or something else?
   - did x86 really directly evolve from the intel 8008?

   would love any links!

   • Julia Evans (b0rk@social.jvns.ca)'s status on Tuesday, 07-Mar-2023 02:07:45 JST Julia Evans

     in reply to

     so far the reasoning I'm getting for the 8-bit byte seems to be:

     1. you want your byte size to be a power of 2. This is EXTREMELY believable to me, but I don't understand why exactly you want this, my understanding of CPU design is very bad. Maybe it's because of busses? (what's a bus?)
     2. 4 bits is too small, you can't fit a character into 4 bits
     3. you also don't want your bytes to be too big, and 8 bits was working well, so the byte size never got bigger after the move from 4 to 8

   • Julia Evans (b0rk@social.jvns.ca)'s status on Tuesday, 07-Mar-2023 02:07:46 JST Julia Evans

     in reply to

     or maybe the reason was that the 8008 was a popular microprocessor, and it happened to use an 8-bit byte so it became the foundation for all of intel’s future microprocessors, but in theory they could have also built a microprocessor with a 10-bit byte instead and that would have been fine too?

     Adrian Cochrane repeated this.