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From: thomas@duteca (Thomas Okken)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Connectix MODE32
Message-ID: <1335@duteca.UUCP>
Date: 29 May 91 00:24:53 GMT
Article-I.D.: duteca.1335
References: <270790.2841D1A9@cmhgate.FIDONET.ORG>
Organization: Delft University of Technology, Netherlands
Lines: 36

From article <270790.2841D1A9@cmhgate.FIDONET.ORG>, by Adam.Frix@p18.f20.n226.z1.FIDONET.ORG (Adam Frix):
> 
> mike@odgate.odesta.com (Mike J. Kelly) writes:
> 
> MJK> What worries me is how Connectix does it (and I haven't heard 
> MJK> anything but generalities here). My uniformed guess is that they 
> MJK> simply replace the dirty ROM code with RAM-based versions. That 
> MJK> makes me nervous because at least ROM-based code can't be overwritten 
> MJK> or destroyed. If this is in fact what Connectix is doing (and 
> MJK> I repeat: I don't really know), I believe having key system routines 
> MJK> in unprotected RAM would make the Mac even more of an unstable 
> MJK> development platform than it already is. 
> 
> Does anyone here know how A/UX handles the problem?
> 
> --Adam--

The Mac ROM consists of the Operating System and the Toolbox. The Toolbox is
a set of convenience routines that run on top of the OS.
When you run A/UX, the OS is replaced by Unix. That is, Mac OS calls are
intercepted and passed on, after appropriate translation of parameters, to
Unix system calls.
The reason that the Mac II/IIx/IIcx/SE30 can't use 32-bit mode under System 7
is that the Memory Manager is faulty - but since the Memory Manager is part
of the OS, which is not used by A/UX, the entire 32-bit clean ROM question
is irrelevant for A/UX users.
BTW, if the vulnerability of RAM-based ROM patched worries you: no Mac System
version uses memory protection to protect system globals or ROM patches.
Since day 1, it has been possible to crash the Mac by corrupting the trap
dispatch tables or patch code. The only way I know of to prevent this is to
use Steve Jasik's "The Debugger", which can use the MMU to write-protect the
system globals and system heap.
(The is, of course, a catch: this feature cannot be used simultaneously with
VM. Sigh. Looks like A/UX is the only way to go if you want both at once.)

 - Thomas (thomas@duteca.et.tudelft.nl)