Subject: Re: ROM 1 vs. ROM 3
Newsgroups: comp.sys.apple2.usergroups,comp.sys.apple2
Followup-To: comp.sys.apple2
From: dempson@actrix.gen.nz (David Empson)
Date: Sun, 7 Feb 1999 19:43:20 +1300
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[Please note that I've crossposted to comp.sys.apple2 and set followups
there.  This discussion is nothing to do with Apple II user groups.]

Charles J. Sarchet <csarchet@ix.netcom.com> wrote:

> The best reason to upgrade to a ROM 3 is if you have an accelerator board
> like the ZipGS or the Transwarp installed, and you are planning to operate
> it at faster than 8 Mhz.
> 
> As I remember, this is the magic number for the ROM 1.  If you accelerate a
> ROM 1 much above that, then you will start to experience multiple system
> crashes.  Why?  well the story I used to get was that the ROM 1 was a single
> layer board and the ROM 3 was a multiple layer board and so on the ROM 3 the
> circuitry could be spread out across multiple layers.  Another story goes
> that the ROM 3 has fewer components on the board. Buzzzz... incorrect.  In
> reality, they are both single layer boards printed on both sides, and the
> ROM 3 actually has more components (although not many more) then the ROM 1,
> however the etching on the ROM 3 is a few microns smaller then that on the
> ROM 1 and the spacing between the etching is a few microns wider and
> therefore can handle the faster clock cycles.

Buzzzz.  Lots of mistakes in there.

1. I'm not aware of significant problems with crashes when using
accelerators above 8 MHz on the 256KB motherboard, though I've never
used one faster than that.  Anyone have any practical experience in this
area?

2. Both the original and 1MB (ROM 3) IIgs motherboards use four layers.

3. The number of components on the two motherboards are pretty similar.
The 1MB motherboard has two ROM chips and eight fast RAM chips compared
to one and four respecitively for the 256KB motherboard.  The 1MB
motherboard is missing several connectors for IIe compatibility, but
there aren't many components associated with them.

4. The 1MB motherboard is generally designed better than the 256KB
motherboard.  It has less induced noise (particularly in the sound
circuitry) and consumes less power than the 256KB motherboard, so the
machine tends to run a little cooler.  This may account for better
accelerator operation.

5. Using an accelerator does _not_ affect the speed of data transferred
over the motherboard.  The accelerator does all high-speed operations
internally, using caching to achieve the speedup.  Access to the
motherboard is controlled by the clocks on the motherboard, which are
exactly the same whether you have an accelerator or not.

> Some other differences that are worth noting:
>
> - the battery on the ROM 1 is soldered to the motherboard, while the ROM 3
> has a battery holder.
> 
> - the ROM 1 can be inserted into an Apple //e case because it has points on
> the board to which the appropriate connectors can be soldered, while these
> have been removed from the ROM 3.  The original upgrade board already had
> the connections soldered in place.
> 
> - the ROM 3 has 1M of Fast Ram instead of the 256K on the ROM 1.

It is also worth noting that with a standard 4 MB memory expansion card,
you get 5 MB of DMA-compatible fast RAM in a ROM 3, compared to 4.125 MB
for a ROM 1.  Both machines can access a maximum of 8 MB of fast RAM,
but there may be compatibility problems.

> - the ROM 3 has a newer and bigger toolbox (although I think most of this
> became obsolete with GS/OS 6.01).

Some of the ROM-based desktop toolsets in the ROM 3 are replaced in
entirety if you run System 6.0 or 6.0.1, but there are still a fair
number being used from ROM (with RAM-based patches for a few calls).

In particular, QuickDraw II has very few changes between System 5.0 and
6.0.1, and runs almost entirely from ROM in the ROM 3.  This produces a
noticeable speed improvement for desktop applications, since ROM
accesses are not slowed down by fast RAM refreshing.


Some other differences that I can think of:

- the ROM 3 has several improvements to the system monitor firmware,
allowing operations like dumping memory over bank boundaries,
disassembly automatically tracks register size changes, simple step and
trace facility built in, etc.

- the ROM 3 (actually the motherboard) supports hardware shadowing of
text page 2, which means that "Alternate Display Mode" no longer causes
a significant slowdown if enabled.

- Sound circuitry has significantly less induced noise from the
motherboard.

- ADB microcontroller in the ROM 3 has built-in support for "sticky
keys" and "keyboard mouse"; these are provided by the Easy Access INIT
for ROM 1, but the software-based version has significant compatibility
problems.

- ADB microcontroller in the ROM 3 automatically updates the Caps Lock
LED on an extended keyboard.  :-)

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

- AppleTalk firmware improvements, particularly in how the slot mapping
is handled.

- RAM disk can be resized without turning the machine off or running a
self-test.  The RAM disk loses the ability to set separate minimum and
maximum sizes, since this feature causes problems.

- Apple 3.5 Drive firmware is noticeably faster (affects ProDOS-8 only).

- One particular signal is provided on slots 1 through 6 instead of just
slot 3, allowing the Video Overlay Card and/or Second Sight to be used
in any of these slots without modifying the motherboard.

- A jumper provides a mechaism for locking out access to the text-based
control panel (intended for classroom situations).

> mrl wrote in message <797eko$ffb$1@remarQ.com>...
> >Question: What is the difference between a ROM 1 Apple //gs and a ROM 3
> >Apple //gs?  I've got a ROM 1 machine, and was wondering if there's any way
> >to upgrade it to a ROM 3 machine, or if such an upgrade is even necessary
> >or practical...

The only way to "upgrade" to a ROM 3 is to replace the entire
motherboard.

Apart from the above details, there are no significant improvements,
e.g. CPU speed.

> >I'm wanting to set it up in the computer room alongside my mac and have a
> >machine that I can use to access the internet and pick up email and read
> >news while my wife does amazing multimedia stuff on the mac.

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