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From: davids@mondo.engin.umich.edu (David Snearline)
Newsgroups: comp.sys.mac.programmer,comp.sys.mac.misc
Subject: Re: ROM in RAM
Message-ID: <1990Oct31.223053.22260@engin.umich.edu>
Date: 31 Oct 90 22:30:53 GMT
References: <1990Oct31.032509.265@bushido.uucp> <891@demott.COM>
Sender: davids@mondo.engin.umich.edu (David Snearline)
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Organization: CAEN, University of Michigan Engineering
Lines: 19

First of all, I believe that Dean Yu was correct in that where the
calls are made from make a big difference.  Ever wonder why the
Technotes say "No tailpatches!"?  It's because of the fact that
the routines do sometimes try to figure out where they have been
called from.  However, my guess is that Accellerator boards compensate
for this -- not hard to do.  Just make sure the addresses look right.

Second, I have a friend who just designed his own upgrade for the Mac,
and he explained how the ROM/RAM situation worked on the earlier Macs.
Apparently, the ROM's went much faster on the original Macs because
the RAM had to slow down for the video display.  Whenever the access
was in ROM, the CPU accessed it full speed since it didn't have to
worry about the display attempting to access the ROM...

--- davids

--
David Snearline				Computer Aided Engineering Network
davids@mondo.engin.umich.edu		University of Michigan Engineering