Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!pacbell.com!ucsd!rutgers!mcnc!borg!hatteras!mccabe
From: mccabe@hatteras.cs.unc.edu (Daniel McCabe)
Newsgroups: comp.sys.mac.system
Subject: Virtual 32-bit clean ROMs
Message-ID: <3336@borg.cs.unc.edu>
Date: 21 Apr 91 02:03:09 GMT
Sender: news@cs.unc.edu
Lines: 25

I keep hearing these reports that I can't have virtual memory beyond 16 MBytes
in my Mac II because my ROMs aren't 32 bit clean (assuming that I've installed a
PMMU in my Mac II).  As far as I can tell, there is no technical reason to 
prevent my Mac II from having a large virtual address space, regardless of the 
ROMs.  Am I wrong?  My guess is that marketing considerations prevent this 
from happening.  Why support old machines when you sell new ones, right?

The beauty of virtual memory is that ALL of your memory can be virtual, not
just your RAM.  One possibility is to make your ROM virtual also.  Simply
load an image of a 32-bit clean ROM from your boot disk into RAM and remap the
the virtual to physical address translation of the ROMs to the RAM containing 
the ROM image.  I would be more than happy to eat 512K of real RAM in order
to get large virtual memory.

I shouldn't even have to upgrade my ROMs in hardware to get 32-bit virtual
addressing.  This should be doable completely in software.

C'mon Apple.  Do it right!  Give all 020+PMMU and 030 machines the ability
to really have 32-bit virtual memory instead of limiting them to a wimpy 
16 MBytes!

Any comments?

Cheers,
danm