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- From: davisson@milton.u.washington.edu (Gordon Davisson)
- Newsgroups: comp.sys.mac.hardware
- Subject: Re: Mac+ and 2-chip SIMMs
- Message-ID: <1992Dec20.020742.8427@u.washington.edu>
- Date: 20 Dec 92 02:07:42 GMT
- Article-I.D.: u.1992Dec20.020742.8427
- References: <1992Dec18.192906.438@otago.ac.nz>
- Sender: news@u.washington.edu (USENET News System)
- Organization: University of Washington, Seattle
- Lines: 23
-
- In article <1992Dec18.192906.438@otago.ac.nz> anadig@otago.ac.nz writes:
- >I understand that 2-chip 1M SIMMs won't work in a Mac Plus. Or an SE, perhaps.
- >Well-known fact. You need 8-chip SIMMs.
- >
- >What I can't figure out is why.
-
- The following is all hearsay, so take it with a grain of salt: the Mac
- Plus, SE, II, and IIx were all designed before the specs for 4 megabit
- chips (the ones used on 2-chip 1MByte and 8-chip 4MByte SIMMs) were set,
- and the 4Mb chips wound up containing a surprise: test mode. I'm not
- sure exactly what triggers test mode (some combination of bus signals
- that didn't mean anything to the 1Mb chips), but it's something the
- older Macs can do by accident. When this happens the memory goes off
- into la-la land, and the Mac crashes.
-
- There are SIMMs that use the 4Mb chips that'll work on older Macs; they
- have PALs that filter the control signals to make sure test mode never
- gets triggered.
-
- --
- Gordon Davisson
- Westwind Computing (206) 632-8141
- 4518 University Way NE, Suite 311, Seattle WA 98105
-