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From: keithd@cadovax.UUCP (Keith Doyle)
Newsgroups: comp.sys.amiga
Subject: Re: Kickstart in ROM
Message-ID: <1878@cadovax.UUCP>
Date: Thu, 19-Nov-87 13:46:32 EST
Article-I.D.: cadovax.1878
Posted: Thu Nov 19 13:46:32 1987
Date-Received: Sun, 22-Nov-87 08:09:13 EST
References: <461@ra.rice.edu> <2802@cbmvax.UUCP> <6594@sunybcs.UUCP> <34127@sun.uucp> <2655@sphinx.uchicago.edu>
Reply-To: keithd@cadovax.UUCP (Keith Doyle)
Organization: Contel Business Systems, Torrance, CA
Lines: 26

In article <2655@sphinx.uchicago.edu> cute@sphinx.uchicago.edu.UUCP (John Cavallino) writes:
.I beg to differ.  Any trap-based routine in the Macintosh OS may be replaced
.at any time. This is possible because all trap routines are accessed through a
.dispatch table in RAM.  There are routines provided to get and set the code 
.address of a routine. Because of this, the replacement code is free to callthe
.old code ifnecessary. The System File contains update code specific toeach ROM
.version. At startup, the boot code determines the ROM version and installs the
.appropriate patches, replacing buggy routines, adding new functionality to 
.existing routines,and even adding routines that weren't present at all in the 
.target ROM. This is how Apple was able to give the Mac Plus (running under the
.most recent system)nearly all of the added functionality ofthe Mac SE ROM with
.out requiring a ROM swap.  The only penalty is that the new code takes up RAM 
.space.  BTW, all such alterations are completely transparent to applications 
.that do not specifically check trap addresses.

Jeez, anyone feel like posting more detailed specs here?  (Mac emulators
anyone?)?

It seems to me the only problem with the "well you can boot a kickstart
into RAM even on the 2000/500" approach, is that you lose 256k or so of
your RAM for applications when doing so.  To people with 512k systems,
that could be pretty significant.  To people who sell RAM boards it's
a feature, not a bug. :-)

Keith Doyle
#  {ucbvax,decvax}!trwrb!cadovax!keithd  Contel Business Systems 213-323-8170