Re: What is the difference between ROM 1 and ROM 3 IIgs computers?

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

Rubywand <rubywand@swbell.net> wrote:

> MERLANCIA writes ...
> > 
> > What is the difference between ROM 1 and ROM 3 IIgs computers?
> > And was there ever a ROM 2 Apple //gs?
> >
> 
>      No "ROM 2" IIgs was released. A few months After the original "Woz"
> signature edition and non-signature (plain case with no "Woz" signature)
> GS release, Apple offered an upgrade which included a new ROM and a new
> Video Controller. The new ROM identifies the upgraded machine as "ROM
> Version 01" near the bottom of the screen.
> 
>      Once GS models were tagged with a ROM number, it became popular to
> refer to original un-upgraded GS's as "ROM-00" machines even though
> these machines do not display any ROM number when started.  

The function that returns the firmware revision does return a value of
zero, so it is quite valid to call this "ROM 0" (or "ROM 00", to follow
the pattern displayed by ROM Version 01).

>      Within a year of the original GS release, in 1987, Apple was
> producing "ROM Version 01" machines which incorporated the upgrade and
> made a few aditional changes to the original motherboard design. Since
> these ROM-01 GS's are not really identical to upgraded originals, they
> were viewed by some as 'using up' a ROM number.

I wasn't aware of any motherboard changes - only the replacement VGC and
firmware.  Can you elaborate?

> When the next significant revision was released in 1989, it identied
> itself as "ROM Version  3".

I think the main reason this was version 3 and not 2 is that Apple had
been releasing confusing documentation with earlier versions.  Early
IIgs technical notes refer to the first two ROM releases as "ROM 1.0"
and "ROM 2.0" (in other words "the first ROM" and "the second ROM"),
when they actually meant ROM 00 and ROM 01 respectively.

Example: IIgs technical note #13 "ROM 1.0 Modem Firmware Bug" describes
a bug in the original firmware that was fixed in what it called "ROM
2.0".

To avoid further confusion, they skipped a number so that ROM Version 3
really is the third ROM release.

A similar jump occurred with the IIc - the original firmware is version
255 (could be regarded as "-1"; this is probably just an unused location
that they later decided to define as the firmware version number), the
UniDisk release is version 0, and the memory expansion card release is
version 3 (the third release).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand