24 Nov
2000
24 Nov
'00
10:17 a.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
I wrote:
Actually, using this metric, the 8080 and Z-80 are
4-bit processors,
Allison wrote:
Where in the world did that come from? The base data
paths for z80
and 8080 are 8bits. Key words are "data paths" as the alu on 8080
is basically 8bits (with microcoded 16 bit ops as two sequential 8bit
ops).
Eric said "width of the (integer) ALU", not "data paths". Note that
I
said in my message that I thought that was a useless metric.
According to its designers, the ALU on the 8080 is 4 bits wide, and
takes 2 cycles for an 8-bit add or subtract. Presumably it takes at
least 4 cycles for a 16-bit add or subtract. The 8080 takes so many
cycles for *anything* that it's not obvious what it does internally on
any given cycle.
Eric