Re: Apple IIgs ROM Disk

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

Bryan Parkoff <BParkoff@satx.rr.com> wrote:

>     I don't see that ROM Disk is used by Apple Computer, Inc.  If it does,
> where can I obtain the information?

Apple never supplied any hardware which provided support for the ROM
disk, but there are third party products that support it.

One example is the OctoRAM ESP card, which is a piggyback card that
attaches to the OctoRAM.  The OctoRAM supports up to 8 MB of RAM using
30 pin SIMMs.  The OctoRAM ESP provides an additional 512 KB of battery
backed static RAM, which is mapped into banks F0 through F7.  The driver
has to be loaded into the card from disk, but after the next restart it
appears as a volume called ROM5, with about 510 KB of storage capacity.
There is a jumper which can be used to write protect the card after the
appropriate data has been written to it, and the battery preserves the
contents while the power is off.

The driver is located at the start of bank F0.  The slot 5 firmware
recognises the presence of a ROM disk by looking for the string
'ROMDISK' at location F00000, and the driver entry point is immediately
after that.  The details are in the IIgs Firmware Reference.

The main problem I had with my OctoRAM ESP is that the NiCd battery was
unreliable, so I ended up removing it from the card and wiring in my own
AA battery pack with separate Nicads, which I attached to the inside of
the IIgs case.

I also found it to be of limited use due to the small capacity: 512KB
isn't enough for a GS/OS boot disk, but it might be sufficient for
ProDOS-8.  If the write protect jumper is connected, it cannot be used
for some software (such as AppleWorks) which requires write access to
the boot disk.

-- 
David Empson
dempson@actrix.gen.nz