Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!yale!eagle.wesleyan.edu!bparsia
From: bparsia@eagle.wesleyan.edu
Newsgroups: comp.sys.mac
Subject: Re: IIci vs. IIcx - Virtual Memory
Message-ID: <20652@eagle.wesleyan.edu>
Date: 3 May 90 17:50:11 GMT
References: <8904@hydra.gatech.EDU>
Distribution: usa
Lines: 49

In article <8904@hydra.gatech.EDU>, gt4586c@prism.gatech.EDU (WILLETT,THOMAS CARTER) writes:
> Here is some clarification of my earlier posting regarding differing
> virtual memory capabilities for the IIcx and the IIci.  According
> to the June MacUser, regarding how much virtual memory your Mac can
> use, "The rule is 14 megabytes minus 1 megabyte for each NuBus card.
> For the SE/30, that means 14 megabytes; forthe Mac II, which has at
> minimum a video card, no more than 13 megabytes can be used.  The
> exceptions are the IIci and IIfx, on which VM will simulate nearly a   
> gigabyte of memory, if you've got the disk space."  These statements
> refer to the virtual memory capability which will be made available
> by System 7.0, whenever it may be released.
	
	I believe that this is incorrect. The "14-1 per slot" rule is for
Connectix' Virtual, not for system 7.0. 7.0 should let you access as much
memory as you have disk space with *any* 68030 (or 68020 + a PMMU). As sys 7.0
is currently non-existing, the only way to get virtual memory is with Virtual.
	The IIci *can* potentially have more VM than the IIcx, if one uses the
on board video circutry rather than a NuBus video card. If VM is all one wants
at the moment, I don't think that the extra megabyte is worth the cost
differential.
	However, I'm confused. I thought that the Mac OS currently supports
*only* 8 megs of memory. Does Virtual patch this in some manner?
	In any case, with system 7.0, all restrictions on memory will be
for all intents and purposes lifted (with the advent of 32-bit memory
addresses).

  I don't know what
> hardware differences exist that allow the IIci and IIfx to do better
> than the other macs.  

As far as virtual memory is concerned, there are none. The PMMU is all you
need, and with the '030, it's what you get.

Does anyone know if the limitations for
> Connectix' Virtual are the same?

See above.
> 
> -- 
> WILLETT,THOMAS 
> Georgia Institute of Technology, Atlanta Georgia, 30332
> uucp:     ...!{allegra,amd,hplabs,ut-ngp}!gatech!prism!gt4586c
> Internet: gt4586c@prism.gatech.edu

Let me know if I have erred. I wish someone official like from Apple would post
a full, clarificatory article on this topic, as I have seen *alot* of
misinformation flying about (of which my current posting may be one).

Bijan J. Parsia