Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!agate!violet.berkeley.edu!steve
From: steve@violet.berkeley.edu (Steve Goldfield)
Newsgroups: comp.sys.mac.hardware
Subject: Re: PMMU question
Message-ID: <1989Oct19.162536.726@agate.berkeley.edu>
Date: 19 Oct 89 16:25:36 GMT
References: <8092@microsoft.UUCP> <kZDC=2y00Uh_02gYA5@andrew.cmu.edu>
Sender: usenet@agate.berkeley.edu (USENET Administrator;;;;ZU44)
Distribution: usa
Organization: University of California, Berkeley
Lines: 28

In article <kZDC=2y00Uh_02gYA5@andrew.cmu.edu> nl0s+@andrew.cmu.edu (Nathan James Loofbourrow) writes:
#>Brian Willoughby <brianw@microsoft.UUCP> writes:
#>> Just a quick question.  If the optional PMMU chip for the Mac II is NOT
#>> installed then how does the address bus get driven?  I'm assuming that
#>
#>This question has an interesting answer (as opposed to all those
#>questions with really dumb answers ;-) )... There's a doohickey known as
#>the HMMU sitting in the PMMU slot of an pre-PMMU'd Mac II. The HMMU
#>apparently followed the previous designs, the GMMU and the FMMU in
#>reverse chronological order; thus its name, as the FMMU was the "Fake
#>Memory Management Unit".
#>
#>Ask for trivia, get trivia. That's how I found this info out.
#>
#>Nathan

But you didn't answer the question. Somebody posted a very
complete explanation about the PMMU, including a description
of what the HMMU does, in comp.sys.mac a few weeks ago. He
said that it does pass through the addresses, which is what
the poster asked. The HMMU (this I know from taking it out
and putting in a PMMU) looks like a plug with 50 or sixty
pins. It seems to be called an 8737A V1475 (I got mine out
and looked at it; it also says 3 4 3-0002-1, copyright
Apple '86 on the back. To be complete, it says VLSI-70 on
the pin side.).

Steve Goldfield