Hellfire wrote:
Does anyone know if all 16 address lines can be used on the memory slot? A
IIGS with 64MB would be nice, but I have always heard that the max
addressable memory was 8MB. Is the upper portion of memory reserved for
anything? Or does the ROM just not support it? If anyone knows, please let
me know.
By the way, I am nearly finished with my 8MB memory card design. So far
it uses only 4 4Mx4 SOJ's and a handful of gates. When it is tested, i will
post the schematics. The nice thing is, it can be built with only about $30
worth of parts and a 16MB SIMM (to scavenge for DRAM's).
Thanks in advance for any help!
The IIgs only allows up to 8.1 megs of RAM (8 megs of "fast" ram, and 128K of "slow" ram). What I recall reading from Apple's Introduction to the IIgs, is that you can put up to 8 megs of RAM in the memory slot, or 1 meg of ROM. I suppose it might be possible to put GS/OS in ROM, but then it would still have to run from the RAM, so other than instance on I don't know what that would do for you. I suppose you could also put applications in that ROM.
Remember how EMS worked with the IBM? There was a 64K block of the "ROM" space on the IBM that was used as a "window" through which code and data could be moved into and out of the 640K area into the EMS RAM which in the early specs had a max of 8 megs, and then it was expanded (16 megs?)
However, at this point in time, there aren't any IIgs programs that need more than 4 megs of RAM, so why bother?
One other point, I seem to recall that DMA to the memory slot is limited to the first 4 megs. Which means things get slow if you expand beyond 4 megs in that slot.
I'm not sure how that works, since I have 7 megs in that slot in my Zipped ROM 3 and 5 (6?) megs in my standard ROM 1.
Roy
-Regards, Matt