classiccmp-digest V1 #163

From: Derek Peschel <dpeschel_at_eskimo.com>
Date: Wed May 10 02:16:23 2000

John Wilson wrote:
> On Tue, May 09, 2000 at 06:39:18PM -0000, Eric Smith wrote:

> > The Macintosh OS has gone through multiple cycles of adding large
> > chunks of new functionality to the System file, then moving those
> > pieces into ROM. Unfortunately when the code gets moved into ROM,
> > it doesn't usually get removed from the System file, because it still
> > is needed for older Macs since Apple typically does not offer ROM
> > upgrades.
>
> I may have this wrong, but I remember being told that this meant having a
> pretty complicated boot process where the ROM versions of various routines
> could be replaced by a newer version off the disk,

Yes, because the ROM is largely made up of resources (i.e., the things you
can edit with ResEdit). The system file on disk is largely made up of
resources too. This may not be so true now as it was (and ResEdit hasn't
been updated in a long time).

> but if you (somehow) pared it down
> to have only the patches required for your particular computer (instead of
> all possible Macs throughout history) you could have a lot more space on
> the disk. Sound right?

Basically, except that the whole thing got an order of magnitude more
complicated after Ssytem 7 came out. Systems 8 and 9 made things even more
complicated and OS X will probably _really_ stir things up. The ROMs on
newer machiens have gone though a lot of changes too; after a certain point
they checked to see if you were booting with System 7 or later and put up an
error if you weren't. I think you can get around this (I've seen it once)
but I'm not sure how.

It's not easy these days to make a universal boot disk. Anyway, it would
have to be a Zip cartridge or CD-ROM (or some other large-capacity medium)
now.

> Wasn't there some point where they dropped support for the early Macs with
> less ROM (64 K vs. 128 K or something??????), or am I making that up? If so,
> was it just because thin Macs didn't have space for the bloat, or was there
> really something wrong with what was in ROM that was beyond help?

I don't know. The issues of (lack of) guaranteed backward compatibility,
in-depth documentation about the OS and ROM, upgradability of the ROMs, and
the possibility of using other OSs are all "knee-jerk reaction" issues to
me. In other words, I don't know the answers, but I suspect they are bad
and gripe accordingly. The documentation I've seen is largely out of date.
The Mac architecture has gone through a large number of changes (some small,
some big). PCI and Open Firmware are promising developments in some ways.
(especially regarding the use of other OSs), however.

I'm a happy Mac user but really out-of-touch with Apple or with Mac
development. Maybe Eric knows more. Eric?

-- Derek
Received on Wed May 10 2000 - 02:16:23 BST