21 Nov
2000
21 Nov
'00
2:27 p.m.
"Eric J. Korpela" <korpela(a)ellie.ssl.berkeley.edu> wrote:
You missed the important one, and the only one that
counts
when determining the bitness of the processor, the width of
the (integer) ALU.
Clearly, regardless of the width of the registers and the
address bus size, the Z80 is an 8 bit processor, as is the
6502. The 8088 and 8086 are both 16 bitters. The 68000 and
68010 are 16 bitters. The 68020 is a 32 bitter as is the
x386.
Actually, using this metric, the 8080 and Z-80 are 4-bit processors,
the IBM 360 Model 30 is an 8-bit processor, the PDP-8/S is a 1-bit
processor, and the IBM 1620 is a zero-bit processor (no ALU).
It's a stupid and mostly useless metric.
Try asking programmers what width processors are instead of hardware
engineers. They'll tell you that the 8080 and Z-80 are 8-bitters,
and that the 68000 and IBM 360 (most models) are 32-bitters.
No, every x86 chip since the original 386 is a 32 bit
CPU since
the width of the integer ALU is 32 bits.
Actually there is a 64-bit integer ALU in most recent x86 processors.
Describing where it is and what it does is left as an exercise to
the reader.
The reality is that there is no single "correct" measure of the
"bitness" of a processor.