From Newsgroup: comp.sys.apple2

Hi guys.
Steve Chamberlin over at BMOW making something like the Laser UDC card: https://www.bigmessowires.com/category/yellowstone/
He posted an interesting question on Retrocomputing SE: How did the IIgs magically slow down to remain compatible with the Disk II Interface card?
https://retrocomputing.stackexchange.com/q/18371/71
I vaguely remembered the speed register bits, but had to do some research to unearth the details - such as which slot ROM bytes the firmware checks. I'm sure many here already know the details, but it was an interesting diversion. I'm a bit surprised though, and wonder why Apple went to so much trouble to support Disk II Interface cards in slots 4 to 7 - but not 1 to 3!
Anyway, first blood with MAME's debugger, and it was up to the task.
Cheers,
Nick.
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From Newsgroup: comp.sys.apple2

In article <99662515-b278-465a-9118-d00f12ebfbccn@googlegroups.com>,
Nick Westgate <nick.westgate@gmail.com> wrote:

I'm a bit surprised though, and wonder why Apple went to so much trouble to >support Disk II Interface cards in slots 4 to 7 - but not 1 to 3!

Slots 1 and 2 were taken by the serial ports and slot 3 was taken by the 80-column firmware. In the ROM 3 IIGS, you can have both internal hardware
and a slot card active and usable in some circumstances, but in earlier revisions, you could only have one or the other. Slots 5 and 6, by
comparison, were normally taken by the onboard floppy controller, slot 4 by
the mouse, and slot 7 by LocalTalk network support (rarely used outside an educational setting, and possibly not even much there).

_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS( https://alfter.us/ Top-posting!
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From Newsgroup: comp.sys.apple2

On Thursday, March 25, 2021 at 5:01:41 AM UTC+10, Scott Alfter wrote:

Slots 1 and 2 were taken by the serial ports and slot 3 was taken by the 80-column firmware.

Sure, that's the typical usage. It's just weird that Disk II Interface cards would have magically worked in the higher slots, and tragically crashed in the lower slots. They could've supported all slots without problem, so I wonder if they did it this way to free up bits in the speed register (unlikely) or free up transistors in the FPI (more likely I suppose).
It was a long time ago, so I forget how well this limitation was known. I'd forgotten - if I ever knew.
Cheers,
Nick.
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From Newsgroup: comp.sys.apple2

"and slot 7 by LocalTalk network support (rarely used outside an
educational setting, and possibly not even much there). "
Ironically, yesterday I reconnected Localtalk on the GS to a G3 running OS9 to fish a file off the HD.
They are in different buildings, and the phone wire goes through the shop, a third building. Total distance is about 400 feet, out of range for 10Base-T ethernet, but not coax (that was 10Base-2, I think) The phone wires are all still there, and phone net still works. Irony 2, I gave up the land line about five years ago.
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