Path: utzoo!attcan!uunet!mcvax!ukc!its63b!etive!lfcs!nick
From: nick@lfcs.ed.ac.uk (Nick Rothwell)
Newsgroups: comp.sys.mac
Subject: Why do Macs have ROMs?
Keywords: Macs, ROMs
Message-ID: <453@etive.ed.ac.uk>
Date: 29 Jun 88 12:36:11 GMT
Sender: news@etive.ed.ac.uk
Reply-To: nick@lfcs.ed.ac.uk (Nick Rothwell)
Organization: LFCS, University of Edinburgh
Lines: 34

I hope this isn't a silly question - it isn't supposed to be. But, I admit to
being a newcomer to the Mac world, so perhaps this is obvious. So: Why do
Macs have ROMs?
   I can see some of the philisophy behind the original 128K Macs. You had some
pretty sophisticated software rattling around inside a tiny skull with access
to 400K of disk, and not much else, so having the graphics and resource
management stuff somewhere safe where you could get hold of it at all times
seemed like a good idea, I guess.
   But things have changed a little. Users are flying 1-2Meg Macs with hard
disks, so memory space and disk access aren't so much of a problem. In which
case, why have a ROM for the OS? Why not just put it somewhere fixed in RAM
instead?
   This question was prompted by a look at the size of the System Files for
System 3.0 and 4.3, which came with my Mac+ recently. System 3.0 is 118K,
System 4.3 is 327K. I suppose 4.3 has MultiFinder hooks and so on, in which
case I can't help thinking that a lot of this code is just bypassing the
original ROM code to make stuff re-entrant (Ok, so that's a wild guess, I
admit). But if the system's heading for 400K, and the ROM is only 128K, and
(I suggest) less and less of the ROM is being used with each system release,
why have it at all? Why not 128K (or less) of Kernel file on the startup disk
instead?
   I can see some need for ROM-based code, of course. You want some bombproof
code to handle system crashes, and something to start it when you switch on!
But the "higher-level" system functions?
   I'm sure there's some easy answer to this. I'm not flaming the approach,
but just curious about how valid it is these days. It would be odd to find a
Sun3 (or generic Unix box) with a ROM to do graphics, so why in a MacII?
   Or am I being naive about the Mac philosophy and mechanics?

Nick Rothwell,	Laboratory for Foundations of Computer Science, Edinburgh.
		nick@lfcs.nd  .ac.uk    !mcvax!ukc!lfcs!ni
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