Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!lfcs!nick
From: nick@lfcs.ed.ac.uk (Nick Rothwell)
Newsgroups: comp.sys.mac.system
Subject: Re: There are 2 different 32-bit modes, folks!  (Was Re: System 7...)
Keywords: System 7, Virtual Memory, 32 Bit Clean
Message-ID: <4224@castle.ed.ac.uk>
Date: 25 May 90 14:18:49 GMT
References: <145253@felix.UUCP> <1990May23.052032.26750@Neon.Stanford.EDU> <2609@wrgate.WR.TEK.COM> <742@earth.cs.utexas.edu> <7249@jarthur.Claremont.EDU> <744@lovelady.cs.utexas.edu> <7258@jarthur.Claremont.EDU>
Reply-To: nick@lfcs.ed.ac.uk (Nick Rothwell)
Organization: Jenny Agutter Appreciation Society of Edinburgh
Lines: 31
In-reply-to: mwilkins@jarthur.Claremont.EDU (Mark Wilkins)

In article <7258@jarthur.Claremont.EDU>, mwilkins@jarthur (Mark Wilkins) writes:
>  I will try to clear up the raging confusion about 32-bit mode and Virtual
>Memory in System 7.

And I think I understand it now, ta...

>  However, all Mac II class machines as well as the SE/30 have what is known
>as 32-bit addressing mode.  This means that if the processor is accessing an
>address, it TRIES to use all 32 bits.

So (correct me if I'm wrong) the only reason this isn't running all
the time is that there is software around which uses the top byte for
it's own ends. A "32-bit clean" program is one that doesn't care that
addresses of things are 32 bit significant. Yes?

I recall from Inside Mac way back when, that handles can have the top
byte reserved (something to do with CDEF's?), so this isn't clean.
I presume there's a tech note explaining what to do these days.

I'm only an occasional Mac programmer, so I don't keep that
up-to-date, but I'm in the process of selling my Mac+ and buying
an SE/30, so I might need to know one day...

>-- Mark

		Nick.
--
Nick Rothwell,	Laboratory for Foundations of Computer Science, Edinburgh.
		nick@lfcs.ed.ac.uk    <Atlantic Ocean>!mcsun!ukc!lfcs!nick
~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~
		   Ich weiss jetzt was kein Engel weiss