Darren New <dne### [at] sanrrcom> wrote:
> >   Just because the 16-bit operations are performed on pairs of 8-bit
> > registers that doesn't make it any less of a 16-bit operation.

> OK. I guess we're just disagreeing about whether that ability makes a 
> CPU an "8-bit CPU" or a "16-bit CPU".

  IMO "16-bit CPU" means "can perform most calculations on 16-bit values
with single opcodes". There are examples of true 8-bit processors where
you really are limited to 8-bit operations (and if you want to calculate
on larger numbers you have to use at least two opcodes, the second one
using the possible flag set by the previous one).

> I mean, I've used mainframes with "string" type opcodes that would 
> operate on 1KBytes at a time. That wouldn't really make them a KByte 
> CPU. :-)

  The question is whether its registers were 1kB in size or not.

  Just because you can fill 1MB of memory with zeros using a single opcode
doesn't tell anything about the bitsize of the registers and how the CPU
uses them.

> >   I understand "8-bit" to mean "has 8-bit registers, and you can only
> > perform an 8-bit operation with a single opcode, because registers can
> > only hold 8 bits of data". Likewise for any other bitsize.

> Well, the 6502 had 16-bit absolute jumps, IIRC. I wouldn't call it a 
> 16-bit CPU.

  Could you calculate eg. additions and substractions using 16-bit values
with single opcodes?

-- 
                                                          - Warp

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