Re: What Are The Differences In The IIGS ROM0 and ROM1 ROMs and Motherboards

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

Paul W. Good <good@primus.ca> wrote:

> What differences are there in the IIGS ROM0 and ROM1 machines?
> 
>      1.  In the ROMs themselves?

Lots of little odds and ends.

The main difference is that ROM 01 has newer versions of the low-level
toolsets (version 2.0 of toolsets 1 through 13, instead of version 1.0),
incorporating a lot of bug fixes.  The majority of these are also fixed
on a ROM 00 machine by running new enough system software (System 2.0 or
later), because the system software loads the patches into RAM at
startup time.

If you are running old system software, the main benefit of ROM 01 is
that it will free up some RAM that would otherwise be occupied by these
patches, and the same bugs are fixed if you run System 1.0 or 1.1 on a
ROM 01.

There is a technical note (TN.IIGS.026) which summarises the changes in
ROM 01 (which it confusingly calls "ROM 2.0").  Apart from toolbox
changes, the other significant ones I can spot from a quick glance
include:

- Detection of disk changes in the Apple 3.5 Drive works correctly.
- AppleTalk bug fixes.
- Applesoft handles horizontal tabbing correctly in 80-column mode.
- Maximum RAM disk size increased to almost 8 MB (instead of 4 MB).
- Interrupt handler bug fixes.
- New monitor command (#) to enable some debugging desk accessories.
- New monitor command (Ctrl-N) to set native mode.
- Serial firmware bug fixes and improvements.
- SmartPort (slot 5) firmware has some bug fixes and better performance.

The most significant difference between ROM 00 and 01 is the fact that
System 4.0 and later (all system software based on GS/OS) will not run
on ROM 00 - it requires ROM 01 (or ROM 3, which has a different
motherboard).

You may run into some old software which only works on ROM 00, because
the software broke the rules about how to use the firmware, or relied on
old bugs which were fixed.

>      2.  In the motherboards?

No difference at all.  All that changed was the ROM chip itself.

There is one point worth mentioning here: early IIgs machines also had a
faulty Video Graphics Controller chip, which could also be upgraded for
free at the same time as the ROM 01 upgrade.

The symptom of the VGC fault was that monochrome double hi-res graphics
mode produced pink fringing effects (it should have been pure black and
white) and/or flickering pixels.  Some machines (including mine)
exhibited the same symptoms in 80-column text mode, with variable
effects depending on the foreground and background colours.

> The location of a file on the Internet describing the differences
> would be great.

If you can find an archive of the Apple II technical notes out there,
have a look for TN.IIGS.026 (in the IIGS folder).  (I have no idea
whether anyone has them online - I have the full set on my Mac's hard
drive, and I only ever accessed them on Apple's FTP site, but they
removed them several years ago.)


If you got your version numbers muddled up and were actually wondering
about the differences between ROM 01 and ROM 3, then that is a different
kettle of fish.  There have been discussions posted here on the subject
in the past, and I could dig through my archives to find one of my
earlier postings.