Re: //gs Memory 8 or 16megs?

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

Roger Johnstone <rojaws@es.co.nz> wrote:

> Bernie to the Rescue has an option to allow the emulated IIgs system to have
> up to 14MB of RAM. The OS and programs will happily use this memory. I think
> the 8MB restriction in a real GS is only in the hardware, not the firmware,
> since even the CDA control panel sees the entire memory and will let you set
> up a RAM disk larger than 8MB.

There are two restrictions:

1. The hardware only regards banks $00 to $7F as being "fast RAM".
Anything above that are either "slow RAM" ($E0 and $E1), "ROM" ($F0 or
higher) or "nothing" ($80 to $DF and $E2 to $EF).  The necessary
addressing signals are not provided to the memory expansion slot in the
"nothing" areas, so a memory expansion card cannot use these areas.

(The TransWarp GS gets around this: it has some extra ROM somewhere in
the $D0-$DF area, but it can do this because it has first crack at
decoding addresses from the processor, before they get to the
motherboard hardware.)

2. The Memory Manager toolset (in ROM) assumes that the fast RAM in the
IIgs doesn't extend past bank $7F.  It would be necessary to patch the
firmware to allow the memory to extend beyond this point.  There is
nothing stopping an emulator from doing this.  (14 MB would be all of
banks $00 to $DF.)

Every other piece of software depends on the Memory Manager for
determining memory limits, so the RAM Disk configuration should
automatically be able to use more than 8 MB if you had a patched memory
manager.