Meaning of "architecture width" - Re: 68K Macs with MacOS 7.5 still in production use...

[Camiel Vanderhoeven]

Op 17 sep. 2016 8:34 p.m. schreef "Guy Sotomayor Jr" <ggs at shiresoft.com>:
>
>
> > On Sep 17, 2016, at 10:10 AM, Chuck Guzis <cclist at sydex.com> wrote:
> >
> > On 09/17/2016 09:23 AM, Eric Smith wrote:
> >
> >> I don't know what the width of the TMS9900 ALU is, but I'm pretty
> >> sure it's not bit-serial, as an add instruction only takes 14 clock
> >> cycles, including four memory cycles. I'd be very surprised if the
> >> ALU isn't either 8 or 16 bits, though 4 might be possible.
> >>
> >> Possibly someone is confused by the bit-serial "CRU' I/O space, but
> >> that is unrelated to the ALU width.
> >
> > Could very well be--I'm just going by other's appraisals of the
> > architecture.
> >
> > But there were some "8 bit" MPUs with bit-serial ALUs, so the question
> > is still valid.
> >
>
> Why?  What does the width of the ALU have to do with the “bitness” of the
> architecture?  If the programmer’s view is 8-bits (or 16 or 23, or ??),
> what does it matter (other than performance) what the width of the
internal
> data paths or ALU are?
>
> It’s interesting from an implementation point of view but not really
> anything else.
>
> In a previous email, I mentioned the IBM 360 as an example of a 32-bit
machine
> (architecture) that had 8, 16 and 32 bit internal data paths and I don’t
think
> anyone would suggest that the 360 models that did not have 32-bit data
paths
> wasn’t a 32-bit “machine”.

Don't forget about the 64-bit implementations, like the model 65.

>
> The same could be said for the PDP-8/s.  That’s a bit serial machine but
it
> is a member of the PDP-8 family.  Would you call it a 1-bit machine or a
12-bit
> machine?
>
> That’s why (in my previous email) I made the distinction between
architecture
> and implementation.  The reference “machine” (which I’ve intentionally
used here)
> is somewhat ambiguous and I tend to use architecture or implementation
when I
> want to be specific.
>
> TTFN - Guy
>