Re: Apple IIgs @ 300mhz

[dempson@actrix.gen.nz (David Empson)]

David Chiu <none@nowhere.org> wrote:

> It might be harder, because then you have work within the constraints of the
> old Apple bus (among other things.) I've always wonder why Apple choose to
> multiplex the bus instead of doing what IBM did with the AT bus (add an
> extra "16 bit" connector in the front of old "8 bit" connector.)

Are you talking about the multiplexing of the bank address onto the data
bus on the IIgs?  That wasn't exactly something Apple had any control
over - it is a feature of the 65816 CPU.

The bank address is not available to the standard slots at all, due to
the timing restrictions of the original Apple II slot bus design.

I agree that Apple could have designed an extended slot for the IIgs,
with the bank address available on the extension (and possibly also some
way of accessing a compatible card in "fast" mode).

If the bank address was available to the cards, Apple could have
designated another area of the address space for each slot, e.g. each
slot could have been given an entire 64KB bank ($E9 through $EF would
have been good candidates), with the possibility of sharing access to a
larger area somewhere above bank $80.

The main disadvantages I can see with the "extended slot" idea is that
it would introduce cards which only worked on the IIgs, which would have
limited their market.

Another problem is that the IIgs would have need a significantly larger
motherboard in order to fit the larger slot connectors, and hence a
larger case.

-- 
David Empson
dempson@actrix.gen.nz