Path: utzoo!attcan!uunet!cs.utexas.edu!usc!jarthur!wilkins
From: wilkins@jarthur.Claremont.EDU (Mark Wilkins)
Newsgroups: comp.sys.mac.hardware
Subject: Re: MacII Memory Limit
Message-ID: <3234@jarthur.Claremont.EDU>
Date: 25 Nov 89 22:36:14 GMT
References: <UZOfAu200UhWE0ol5Z@andrew.cmu.edu> <6688@merlin.usc.edu>
Reply-To: wilkins@jarthur.UUCP (Mark Wilkins)
Organization: Harvey Mudd College, Claremont, CA
Lines: 26

In article <6688@merlin.usc.edu> malczews@girtab.usc.edu (Frank Malczewski) writes:

>by a ROM upgrade.  The problem pertains to the fact that 4MB and larger
>SIMMs follow a standard different from the one Apple had anticipated
>when the II and the IIx were made available.  The note goes on further
>to say that you will be pretty much stuck with 8MB max, and that no
>fix (i.e., recall) is likely on Apple's part.

   Apple made certain assumptions about the 4mb chip standards when they
designed the Mac II series which turned out to be false.  Specifically they
did not anticipate the addition of a test mode which was activated with each
interrupt on the Mac II.
   Apple suggested that manufacturers could use custom logic to mask out
the set of signals which activate this test mode.  Also, the IIcx, SE/30,
and IIci have been fixed in such a way that this mode is not activated, so
any 4mb simms with or without such logic will work in these machines.
   Also, the boards which are being sold which use 32 1mb chips to provide 4
megs will work in any machine which can handle that much memory.

   HOWEVER:
   A ROM upgrade is indeed necessary for the original Mac II to use ANY TYPE
of 4mb simms.  The only way to get this upgrade is to buy the SuperDrive 
upgrade.  I think the Tech Note describes this as "mysterious" or something.

  -- Mark Wilkins
     wilkins@jarthur.claremont.edu