Re: Buying a used IIgs ...

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

In article <C859Io.CFp@eskimo.com> lurch@eskimo.com (Erik Kloeppel) writes:
> I have just one thing to add... the ROM 1 can address 8megs RAM DMA ( if 
> you find you need that much), whereas the ROM 3 is limited to 6 MEGS DMA.

Where did you get those numbers from?

The IIgs supports DMA to four rows of memory on the memory expansion
card, plus the motherboard RAM.

This means that for a card using 1 megabit RAM chips, cards up to 4
megabytes are DMA compatible.

Thus, a ROM 1 can support DMA to 4.125 megabytes (plus slow RAM) and a
ROM 3 can support DMA to 5 megabytes (plus slow RAM).


Some memory expansion cards claim to be able to support DMA up to 8
megabytes.  I don't believe them.

The RAMFast SCSI card also claims it can do DMA up to 8 megabytes.  I
do believe it.

I've heard that the Apple High-Speed SCSI card (at least, the GS/OS
SCSI Manager) knows not to try doing DMA past 4 megabytes, so it isn't
a problem anyway.  Disk I/O just slows down past the 4 megabyte limit.


The only problem with a ROM 03 with lots of RAM is that you can't
create a RAM disk if you have 8 megabytes of RAM, due to a bug in the
ROM.  If you have 7 megabytes or less, there is no problem.
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand