Virtual vs Physical memory (was Re: Designing around a 6502 ))

From: Eric J. Korpela <korpela_at_ssl.berkeley.edu>
Date: Thu Feb 13 18:47:00 2003

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> ----- Original Message -----
> From: "Eric Smith" <eric_at_brouhaha.com>
> To: <cctalk_at_classiccmp.org>
> Sent: Wednesday, February 12, 2003 1:57 PM
> Subject: Re: Virtual vs Physical memory (was Re: Designing around a 6502 )
>
>
> > > PS Is the 6809 a 8 or a 16 bit CPU?
> >
> > Yes.
>
> :-) Good Answer
>
> This has been argued many times. Personally, I would go with the width of
> the accumulator(s), 8 bits for 6809, even though there are special (or
> perhaps BECAUSE they are special) instructions that use the combination of
> the two accumulators as one 16 bit ("D") register.

I tend to agree, but I would specialize that even further. As time goes on,
I become more convinced that ALU width should be the determinant of bittedness.
The 6809 requires multiple ALU passes for a 16 bit operation because the ALU
is 8 bits wide. The 68000 is a 16 bit processor for the same reason.

I seem to recall that that makes the 8080 a 4 bit CPU, though.

Eric
Received on Thu Feb 13 2003 - 18:47:00 GMT