Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!brutus.cs.uiuc.edu!apple!agate!helios.ee.lbl.gov!ncis.tis.llnl.gov!lll-winken!arisia!sgi!shinobu!odin!maddog!pkr
From: pkr@maddog.sgi.com (Phil Ronzone)
Newsgroups: comp.sys.mac.hardware
Subject: Re: PMMU question
Message-ID: <1076@odin.SGI.COM>
Date: 24 Oct 89 17:47:58 GMT
References: <27044.2543231E@cmhgate.FIDONET.ORG>
Sender: news@odin.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 28

In article <27044.2543231E@cmhgate.FIDONET.ORG> Adam.Frix@f200.n226.z1.FIDONET.ORG (Adam Frix) writes:
>Nathan James Loofbourrow writes:
> 
>I recently flipped through a very new (1989) book about the Mac II
>(obviously written before the 030 machines came out, but published
>afterwards).  It was allegedly a technical treatment of the machine, but I 
>didn't look at it that closely.  What I did read was that HMMU stood for
>"Hochsprung Memory Management Unit" or some such thing.  Now, I know
>perfectly well that the Deep Shit Manager has been referred to a few other 
>ways by people not in the know (Desperate Situation Manager, etc.), so
>I'll use this bandwidth to ask:  was the author of this book just spouting 
>off, because he didn't know any better?  I mean, F,G,HMMU sounds so
>simple--and, of course, the simplest explanation is usually the correct
>one--that I'm questioning this Hochsprung MMU thing.

The Mac II was designed by Mike Dhuey and Ron Hochsprung, and made to work
by Ron Hochsprung. Ron did the simple idiot chip known as the HMMU, and yes,
the H stood for Hochsprung.

BTW - the HMMU does NOT simply pass the address lines through. It maps some
addresses, and most importantly, chops off the high order byte so that the
24-bit idiot apps don't blow up. For a long while, we called the HMMU the
"fake MMU". There was also an MMB, but that is another story ...

-------------------------------------------------------------------------------
Phil Ronzone   Manager Secure UNIX           pkr@sgi.COM   {decwrl,sun}!sgi!pkr
Silicon Graphics, Inc.               "I never vote, it only encourages 'em ..."
-------------------------------------------------------------------------------