Re: Whether something is RISC or not (Re: PDP-8 theology, not Concertina II Progress)

On Wed, 2 Oct 2024 16:08:43 +0000, Brett wrote:

David Schultz <david.schultz@earthlink.net> wrote:

On 10/1/24 3:00 PM, Thomas Koenig wrote:

MitchAlsup1 <mitchalsup@aol.com> schrieb:
>

A 32-bit bus would have priced the 68K at 30%-50% higher simply
due to the number of pins on available packages. This would have
eliminated any chance at competing for the broad markets at that
time.

>
Would have an external 16-bit bus and an internal 32-bit bus have
been advantageous, or would this have blown a likely transistor
budget for little gain?

>
Saving an extra pass through the 16 bit ALU for a 32 bit operation would
be faster. Assuming that you didn't have to wait for another bus cycle
to get the other half of an operand.
>
Making it faster for register to register operations and not much else.

>
A 16 bit barrel roller does not make sense, and Motorola had no idea
that shifts would be so important.

In the original 68000, a barrel shifter would have blown the area
budget--it would have been about equal to the d-section; even in
16-bit form. Remember this was a 1 layer metal design before poly
silicon was in the process.