Re: ROM1 --> ROM3 upgrade?

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

In article <isaksos-3107951526490001@isakson.198.159.in-addr.arpa>,
Steve Isakson <isaksos@macmail.mcgawpark.baxter.com> wrote:
> Can a IIgs with ROM1 be upgraded to ROM3?
> 
> What do I have to change to upgrade?

The whole motherboard.  It is not possible to "upgrade" a ROM 1 to a
ROM 3 via any simpler method.  Alltech Electronics sells a motherboard
upgrade for something like US$195.

> What's different/better about a ROM3 machine?

The major difference is the extra memory.

Most of the changes are insignificant or cosmetic, and the vast
majority can be gained on a ROM 1 by using the latest system software.

There are lots of little changes to the ROM 3, none of which are
particularly significant.  A few that come to mind:

- more "fast" RAM (1 MB instead of 128 KB).  This increases the maximum
  DMA-compatible RAM to 5 MB, instead of 4.125 MB on a ROM 1.  Both
  machines have an upper limit of 8 MB of fast RAM.
  Both machines also have 128 KB of "slow" RAM and 64 KB of sound RAM.

- more ROM (256 KB instead of 128 KB).  Most of the additional ROM space
  is used for toolsets that are loaded from disk on a ROM 1.

- less electrical noise, so sensitive cards might work better, and
  there is less noise in the sound outputs.  Power consumption is
  somewhat lower.

- keyboard micro has "keyboard mouse" and "sticky keys" built in.
  They can be added via software on a ROM 1, but have compatiblity
  problems.

- keyboard micro automatically updates the Caps Lock indicator on an
  extended keyboard (this can be done in software on a ROM 1, but it
  has speed penalties for the computer).

- faster 3.5" drive and RAM disk firmware (only relevant for 8-bit
  software).  RAM disk no longer supports "minimum" and "maximum"
  sizes, which never worked safely anyway.  RAM disk may be resized
  at reset time much more easily.

- changes to AppleTalk firmware so that it lives in the slot it is
  actually using, rather than borrowing the "screen holes" of that slot.

- Slot 4 can be set to "Your Card" without losing access to the mouse in
  GS/OS programs (you still lose it in 8-bit software).

- More control panel options for mouse tracking speed.

- The system monitor (CALL-151) has several new features, including bank
  wrapping, step/trace commands and improvements in the disassembler.

- An extra signal is provided on slots 1 to 6, which allows some video
  cards (Second Sight and Video Overlay Card) to be used in any of these
  slots, whereas only slot 3 provides this signal on a ROM 1.

- Hardware shadowing support is provided for text page 2 (which is very
  rarely used), instead of the software shadowing used by the "Alternate
  Display Mode" on the ROM 1 (which slows the machine down quite
  noticeably).

- Newer versions of the low-level toolsets in ROM, saving RAM that is
  required in a ROM 1 to load patches.  The ROM 3 also gets a slight
  speed benefit here, because code runs faster in ROM than in RAM.  The
  most noticeable difference is faster graphics display in desktop
  programs, by about 5% to 10% over a ROM 1.

- Several high-level toolsets are in ROM, saving more RAM, load time
  and improving speed further.


There are a very small number of programs that don't work properly (or
at all) on a ROM 3.  I have only ever encountered one of these (an
animated watch utility) and a newer version fixed the problem.

The incompatibilities are generally due to programs breaking Apple's
rules on ROM entry points - calling undocumented routines or bypassing
the documented entry points, or by accessing undocumented memory
locations in system RAM.  The affected programs tend to be older games
and demos.  Similar problems occurred when the ROM 1 came out, with
programs making assumptions about ROM 0.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand