Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!blkcat!Uucp
From: Charlie.Mingo@p4218.f421.n109.z1.FidoNet.Org (Charlie Mingo)
Newsgroups: comp.sys.mac.misc
Subject: Re: Mac Vs. Windows? (sorry)
Message-ID: <674648116.0@blkcat.FidoNet>
Date: 19 May 91 00:54:27 GMT
Sender: Uucp@p0.f40.n109.z1.FidoNet.Org
Lines: 23

mariusk@Lise.Unit.NO (Marius Kjeldahl) writes:

MK> 1. Usually RAM is faster than ROM, thats why they incorporate things like 
MK> shadowram and so on.

     RAM may be slightly faster than ROM in the MS-DOS world, but on Macs the 
opposite is true.   Also, the comparison of ROM to RAM is a bit off, as with RAM 
the code has to be loaded from disk in the first place.  If you had gobs of RAM 
to spare, you could just preload the whole thing at boot-time, but the ROM on my 
Mac IIci is 512K, which would consume most of MS-DOS's 640K address space.  If 
you don't preload, then ROM is thousands of times faster than any disk access.

MK> 2. That is one of the drawbacks with the operating system in ROM - you'll
MK> usually need hardware to perform the upgrade. This kind of solution you are
MK> mentioning does not sound healthy.

     Some of the MacOS is in ROM, the rest is put in the "System" file on the HD.
ROM overrides are fairly rare, and simply consist of a tweak substituting a RAM-based code segment for a ROM-based one.  Owing to the design of the 680x0
series, this is easily accomplished by changing a single low memory value in
the trap dispatch table.  ROM overrides are a complete nonissue in the Mac world.


 * Origin: mingo@well.sf.ca.us  mingo@cup.portal.com (1:109/421.4218)