3 ms·

Some VAXen could also do 128-bit ALU operations too. I thought DEC had a full 128-bit CPU but I've never been able to find it... I probably just remember wrong.

• PaulHoule 5y ago
  Of the various claims that something is X-bit I think the most credible is the size of the address space as opposed to the size of the ALU. A 128-bit address space is large enough (UUIDs) that you can name 2^64 objects (about as many iron atoms are as in an iron filing) randomly. That lets you take two separate systems and then merge them into one system with no name conflicts, a handy property for 'distributed systems'
  • kens 5y ago
    That would yield a mess, historically. For instance, the 32-bit IBM System/360 had a 24-bit address space. The 16-bit Intel 8086 had a 20-bit address space. The 4-bit Intel 4004 had a 12-bit address space. It doesn't make sense to call the 4004 a 12-bit processor and the System/360 a 24-bit processor.
  • duskwuff 5y ago
    > Of the various claims that something is X-bit I think the most credible is the size of the address space as opposed to the size of the ALU. But that would make the MOS 6502 a 16-bit processor, and the Intel 8088 20-bit (!) -- neither of which are consistent with common usage. (They're generally considered 8-bit and 16-bit, respectively.) I'd stick with "the size of a general-purpose register". That neatly excludes special-purpose registers from consideration, like 256/512-bit AVX registers in x86_64 systems and the 16-bit program counter in most 8-bit CPUs.