Re: I have a IIgs. So now what?

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

Michael Black <et472@FreeNet.Carleton.CA> wrote:

> David Empson (dempson@actrix.gen.nz) writes:
> > Tristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:
> > 
> >> I'll have to dig the computer out of the shed one day. It's in a special
> >> padded carrybag with spaces for the keyboard and mouse. I seem to recall
> >> that it may also have the OS built into ROM.
> > 
> > That's basically true for all Mac models prior to the iMac.
> > 
> But the Classic had the whole shebang in ROM.  So if you pressed
> the right keys while starting up, you didn't need the OS on floppy or
> the hard drive.

It would have been implemented with a ROM disk that contained the system
folder and whatever applications they decided to include. It was
probably enough to run Finder and disk repair tools but not much more.

I don't see that as being any different to including a bootable floppy
or CD containing disk repair tools. A lot harder to lose the CD. :-)

With a read-only system folder and startup volume, many applications
won't work. At the very least they wouldn't be able to save their
preferences, and you can't "install" anything.

They could have done it as a RAM disk which is initialed from a ROM
image, but that doesn't achieve anything significantly different.

Incidentally, the IIgs can also support a ROM disk, if you have a memory
expansion card which implements ROM or battery backed static RAM in the
$F0 to $F7 banks. 512 KB isn't enough to boot GS/OS, however. It could
grow into banks $F8 through $FB ($FD on a ROM 1) if you broke the rules
- that area was reserved for expansion of the motherboard ROM.

I had an OctoRAM memory card with the OctoRAM ESP piggyback card that
implemented a ROM disk in static RAM with backup battery. It worked
quite well for limited use (and was great for 8-bit software, e.g.
AppleWorks in ROM) until the battery died and I found other uses for the
static RAM.

> The only Mac that did that, and I suspect they realized the flaw.  No easy
> way to upgrade it, 

It was "upgraded" by booting from a floppy or hard drive containing
later system software, which would have run newer system software (and
applications) while booted from that disk. If the new system software
wasn't too much later than the original version in the ROM then it would
have used patches to replace portions of MacOS out of ROM, but it would
not use anything from the ROM disk (including the system folder or ROM
applications).

You could still revert to the original version by booting from ROM.

> which is likely why they didn't use that method before, or after.

I can think of several reasons why they didn't continue with the idea in
later models:

- Cost: ROM was expensive, and the ROM disk would have got larger as the
minimal system file, Finder and other applications grew with later
versions.

- There might have been memory space issues, as the ROM disk would have
been sitting there most of the time unless they bank switched it in
(replacing part of the address space reserved for RAM).

- The "moving target" issue: putting the system file and applications in
ROM might mean they needed to be frozen at an earlier point in the
production cycle than if they were supplied on CD or floppy. This gives
less scope for last minute fixing of bugs. The ROM was usually not
updated after the initial release of a model, but the system software on
floppy could be kept up to date and later machines could have a later
system on disk.

- Too many constraints on what you could do while booted from ROM (like
when you boot from CD).

As flash ROM is getting cheaper, it might be appealing to offer this
again in a future Mac model. A bootable ROM disk containing a minimal
Mac OS X and disk repair tools (like the install CD but without the
installer and a different front end, possibly even a simple Finder)
might be about 300 MB. As this is in flash ROM, it could also be
upgraded in the same manner as a firmware update.

-- 
David Empson
dempson@actrix.gen.nz