4 ms·
I'd say, more importantly, it has an 8-bit data bus. It is the 4 bit address bus which cripples it. By comparison, the 4004 has a 4 bit data bus and 4 bit regis
by tr352 11y ago
I'd say, more importantly, it has an 8-bit data bus. It is the 4 bit address bus which cripples it. By comparison, the 4004 has a 4 bit data bus and 4 bit registers, but a 12 bit (4KByte) address bus.
- kosma 11y agoHow about implementing some sort of paging on top of it, Intel-style?
- tr352 11y agoIt seems like it can also easily be extended to an architecture with 12 bit address bus. Simply extend the size of every instruction to two bytes, and use the extra byte to refer to a 12 bit instead of 4 bit address.
- userbinator 11y agoThe Pentium has a 64-bit databus, yet its general-purpose registers are only 32 bits and it is classified as a 32-bit machine. This gets even muddier with the Pentium MMX, which has a set of 64-bit MMX registers. Of course there's also 80-bit-wide registers in the FPU of everything back to the 8087... Bitness is a surprisingly subtle thing to define, but I think an 8-bit-wide GPR is enough for this one to be called 8-bit.
- dspillett 11y agoYeah, it is a pretty muddy area when you actually look at the details, but it is generally accepted that the bit-ness of a CPU is related to its general purpose register size. The general purpose registers can be thought of as the processing unit's native size (sometimes called the word size). Anything else (data buses, address buses, special purpose registers for floating point or vector operations, and so forth) can and will vary. Take the 80386SX for another somewhat convoluted example: 32-bit general purpose registers so considered a 32-bit CPU, but some of those registers are effectively composed of chunks that can be used independently to work with 8 or 16 bits at a time, it has a 24-bit address bus, and a 16-bit data bus (which uses multiple requests when asked to bring or push a 32-bit value - this was the primary difference between the 386 (later dubbed 386DX) and 386SX models).
- tr352 11y ago> The Pentium has a 64-bit databus Didn't realize that, and you're right. Other examples of CPU's that I'm aware of with a different "bitness"/databus width are the 68008 and 8808, but in both cases the data bus is smaller than the "bitness".
- cmrdporcupine 11y agoSure, or the 68k itself which has a 16bit physical data bus but 32bit registers, spawning 30+ years of pointless arguing over whether to classify it as 32 bit or 16 bit.