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From: cute@sphinx.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Kickstart in ROM
Message-ID: <2655@sphinx.uchicago.edu>
Date: Wed, 18-Nov-87 01:00:48 EST
Article-I.D.: sphinx.2655
Posted: Wed Nov 18 01:00:48 1987
Date-Received: Fri, 20-Nov-87 23:13:33 EST
References: <461@ra.rice.edu> <2802@cbmvax.UUCP> <6594@sunybcs.UUCP> <34127@sun.uucp>
Reply-To: cute@sphinx.uchicago.edu.UUCP (John Cavallino)
Organization: U Chicago Computation Center
Lines: 24
Summary: not quite!

In article <34127@sun.uucp> cmcmanis@sun.UUCP (Chuck McManis) writes:
>Amiga and Commodore have devised what I consider to be an extremely clever
>and workable way to sell machines with the bulk of the O/S in ROM and yet
>keep open the door for easy improvements and cost effective updating.
>
>Nobody else in the Computer business has managed to do that.
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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 call the
old code if necessary. The System File contains update code specific to each 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 of the 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.
-- 
...ihnp4!gargoyle!sphinx!cute
(insert pithy quote here)