Path: utzoo!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!mailrus!ames!amdahl!pyramid!voder!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac
Subject: Re: Why do Macs have ROMs?
Keywords: Macs, ROMs
Message-ID: <13155@apple.Apple.COM>
Date: 1 Jul 88 18:06:00 GMT
References: <453@etive.ed.ac.uk>
Reply-To: lsr@apple.apple.com.UUCP (Larry Rosenstein)
Organization: Advanced Technology Group, Apple Computer
Lines: 37

In article <453@etive.ed.ac.uk> nick@lfcs.ed.ac.uk (Nick Rothwell) writes:
>   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

As has been discussed recently, I don't think the majority of users have
more than 1Mb.  I don't know what percentage have hard disks.  All the
discussion about FullWrite, HyperCard, LSC, ... taking 1Mb or more means
that RAM space is still at a premium.

On a Mac Plus, there are only about 30K of patches.  Putting everything in
RAM would require an additional 80-90K of RAM.  Plus there would be
increased boot time while the stuff was being loaded.

>   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

Looking at the System file size is misleading.  The System file contains
patches for 3 different machines, plus fonts, color resources, etc.  It is
difficult to squeeze everything onto 1 800K disk as it is now, it would be
almost impossible to release a bootable system if it also had to include the
ROM image (especially for a Mac II with 256K of ROM).

I don't think much of the ROM code is "wasted" (ie, not used), and the
percentage is not constantly increasing.  Of the changes made in System 6.0
vs. System 5.0, most were additions to the ROM (eg, Notification Manager,
Sound Manager for Mac Plus/SE), rather than replacements for ROM routines.

Another historical reason for the ROM is that on all the Macs before the Mac
SE and Mac II, the video circuitry was competing with the CPU for the RAM.
Therefore, code running out of ROM ran faster than out of RAM.  

		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 27-AJ  Cupertino, CA 95014
	    AppleLink:Rosenstein1    domain:lsr@Apple.COM
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