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From: alan@pdn.UUCP (Alan Lovejoy)
Newsgroups: comp.sys.mac
Subject: Re: Virtual Memory with the Mac OS
Message-ID: <1514@pdn.UUCP>
Date: Tue, 13-Oct-87 09:52:56 EDT
Article-I.D.: pdn.1514
Posted: Tue Oct 13 09:52:56 1987
Date-Received: Thu, 15-Oct-87 06:24:27 EDT
References: <2653@okstate.UUCP> <2542@batcomputer.tn.cornell.edu> <1478@pdn.UUCP> <6453@apple.UUCP>
Reply-To: alan@pdn.UUCP (0000-Alan Lovejoy)
Organization: Paradyne Corporation, Largo, Florida
Lines: 18
Keywords: virtual memory 68851 HMMU wait states

In article <6453@apple.UUCP> north@apple.UUCP (Donald N. North) writes:
>For the record, the HMMU (an Apple custom, not a 68461) adds ONE wait state
>to each basic memory access; when it is replaced with a PMMU (68851) TWO wait
>states are added to each memory access.  Thus it only pays to use the 68851
>when you really need it (ie, for A/UX).  It not only costs you $$ but degrades
>performance too.
>-- 
>
>Don North
>Apple Computer, Inc.
>Advanced Technology Group

It appears my sources were wrong (I've never looked inside a Mac II
myself).  One of my sources also maintains that two wait-states are
necessary for mother-board memory accesses so that NuBus devices can
access it.  Is there any truth to this (now I doubt everything!)?

--alan@pdn