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From: info-mac@uw-beaver (info-mac)
Newsgroups: fa.info-mac
Subject: FatMac memory map?
Message-ID: <2392@uw-beaver>
Date: Sat, 1-Dec-84 07:30:09 EST
Article-I.D.: uw-beave.2392
Posted: Sat Dec  1 07:30:09 1984
Date-Received: Tue, 4-Dec-84 06:34:41 EST
Sender: daemon@uw-beave
Organization: U of Washington Computer Science
Lines: 27

From: David.Anderson@CMU-CS-K.ARPA
I would like to construct an environment on my FatMac that looks
exactly like a 128K machine for testing out applications that I write
distributing them.  Has anyone figured out how to do this?

I know that the screen and sound buffers are shifted up by $60000, but
I've been peeking around in memory to find out what else is different.
The only other difference that I see is that the system heap extends
from $B00 to $CB00, for a total of 48K bytes, vs. only 16.5K on the
smaller Mac.  Why and how is this done?  My guess is that this is
probably done by one of the 3 original INIT resources in the system --
anyone know for sure?

Another point of concern is the RamDisk -- I wonder if I've found a
bug.  The INIT 3 resource slides BufPtr down to $28000, and I see in
the RamDisk sources that it occupies $50000 bytes, or out to $78000.
However, when running without the RamDisk, but with MacsBug, BufPtr is
$76640.  It appears to me that if you fill up the RamDisk you'll
overwrite part of the debugger.

P.S.  I've found that many of the PD programs I have don't work on my
FatMac -- dbrothers' music engine, the Clock with numbers that
transform before your eyes, and others.  (And I found out the hard way;
I offered to have my Mac play some music for a guest, and after waiting
for it to initialize the waveforms, etc., out came nothing.)  If you do
your own screen or sound hacking, make sure to use the $7a700 and
$7fd00 addresses -- they'll map around on a 128K Mac.