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

[Rubywand <rubywand@swbell.net>]

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.  

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

     There are many differences between the ROM-01 and ROM-03 GS. Few of
these are of much importance. One ROM-03 advantage is a less noisy, less
glitch-prone Slot Card bus. The most significant difference is that the
ROM-03 has 1MB of on-motherboard 'main system RAM' whereas the ROM-01
has 256kB. The ROM-03 can be upgraded to 5MB of true main system RAM
whereas the ROM-01 can be upgraded to 4.25MB of true main system RAM.

     Both the ROM-01 and ROM-03 can be upgraded to a max of 8MB 'main
RAM'. This may seem to eliminate the ROM-03's mem size advantage; but,
there are still a few questions about how accessible the extra 4MB or
3MB of main RAM may be. Using the extra RAM involves employing a kluge
to create an address line at the Expansion Memory Slot-- so, at the
least, it appears that you take an access speed hit.  This is why Apple
hardware manuals specify that 4MB is the maximum size of Expansion Slot
RAM. For no-questions, full-speed-access RAM, the ROM-03 GS has a 775kB
advantage vis-a-vis a ROM-01 GS.


     Most IIgs's in use today (including ours) are ROM-01 machines.
There is no significant ROM-03 advantage in terms of being able to run
ROM-03-only software because those who write programs can not very well
take advantage of ROM-03-specific features if they want their stuff to
be of general interest to most GS users. Meanwhile, there are a few old
GS wares which will not run on the ROM-03 GS.

     On the whole, there is really no question as to which base design
is better. The ROM-03 is newer technology with more on-motherboard RAM.
If you do not mind paying more, a ROM-03 GS is the one to get.    

     

Rubywand