Subject: Re: ROM 1 vs ROM 3???
From: spec@vax2.concordia.ca (Mitchell Spector)
Date: Mon, Sep 28, 1998 058 [L
Message-id: <28SEP199803582149@vax2.concordia.ca>

In article jgreer4350@aol.com (JGreer4350) writes...

>I don't understand the difference between the two. Is one better or more
>compatible?

    Well to an outsider (anyone totally unfamiliar with the Apple II)
the differences are rather insignificant and trivial. For the most
part, it could be summed up as the same original Apple IIgs computer,
only with more built-in RAM and ROM. That observation wouldn't be too
far off the mark, as the Apple IIgs--as manufactured and shipped from
Apple--remained relatively unchanged throughout its 6+ year lifespan.

    As for a detailed explaination of the differences, here they are
in a nutshell: The first motherboard revision of the Apple IIgs had
256K built-in, 128K of ROM. The original firmware that plugged into
this board was known as the "ROM 00", which was then replaced by the
"ROM 01" firmware (which Apple offered as a free update by simply
swapping a single ROM chip).

    The next motherboard revision was called "The Apple IIgs with
1 Megabyte of RAM" and as the name implied, came with just over a
1 MB of memory built-in (1152K to be exact--both machine had 128K
of 'Slow RAM', but the ROM 00/01 had 128K for 'Fast RAM' while the
ROM 3 had 1024K. So 128K+128K=256K or 128K+1024K=1152K). It also
had double the ROM size, totaling 256K (the ROM 00 and 01 firmware
was only 128K) and as the third revision of the firmware, Apple
decided to call it the "ROM 3" (rather than ROM 02). The new board
also featured a newer ADB micro (built-in keyboard mouse, sticky
keys, updating of extended keyboard LEDs), the MB0 signal required
by video cards available in slots 1 through 6 (rather than just
slot 3 on the old board), hardware shadowing of text page 2, a
removable clock battery, a set of jumper pins to lock out the
classic text Control Panel and decreased electrical noise and
power consumption, so it had cleaner sound and more likely to
work with sensitive cards.

    As for the firmware changes, they added many more toolsets in
ROM and updated existing ones (System 5 versions), gave it faster
3.5 drive and RAM Disk firmware when used in 8-bit mode, made it
so you could set slot-4 to 'Your Card' without losing the mouse in
GS/OS and made it so AppleTalk less was constricted in terms of slot
assignment. They cleaned up the Classic text Control Panel, let you 
warm-boot to resize RAM Disks, added new System Monitor features, 
and of course, many bug fixes (and new bugs added). :)

    In summary, the ROM 3 board was slightly faster (maybe 5-10%)
when running native software and gave you many small benefits you
did not get with the ROM 00/01 board (being able to have 5 MB of
DMA memory was an obvious one, not having that annoying buzzing
and hissing from the Ensoniq chip or using a 15 MHz Zip GS were
a couple more worth mentioning). Originally there were compatibility
issues with older software titles, just like when the ROM 01 was 
released, but anything worthwhile has been updated or patched
by now. It was mostly hardcoded games and demos that had problems
with the new ROM. All this is off the top of my head, so I may
have missed a couple of things, but that should give you a good
idea.

Mitchell Spector
spec@vax2.concordia.ca