Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!sdd.hp.com!hplabs!hpcc01!hp-ptp!davew
From: davew@hp-ptp.HP.COM (Dave_Waller)
Newsgroups: comp.sys.mac.system
Subject: Re: There are 2 different 32-bit modes, folks!  (Was Re: System 7...)
Message-ID: <9390003@hp-ptp.HP.COM>
Date: 25 May 90 17:07:45 GMT
References: <7258@jarthur.Claremont.EDU>
Organization: HP Pacific Technology Park - Sunnyvale, Ca.
Lines: 33

mwilkins@jarthur.Claremont.EDU (Mark Wilkins) writes:
> 
>     Note that Virtual Memory can get you up to 16 megabytes WITHOUT 32-bit
>     cleanliness of any sort.  (What's 2^24?  Anyone?  Anyone?)  Note that
>     each NuBus card takes up 1 megabyte of the bottom 16 in the address
>     space, and that the ROM takes up another.

Let me see if I have this straight -- My IIcx (purchased in March... I
assume it has the latest ROMs available for the IIcx) uses a memory
manager that has 24 bits of addressing. This is 16MB of address space.
Does that mean that I can address 16MB of Virtual Memory on my 4MB
system?

But "no", you say, "each NuBus card takes up 1 megabyte of the bottom
16 in the address space, and that the ROM takes up another."  What
exactly does this mean?  I interpret "bottom 1MB" to mean addresses
0x000000 - 0x0FFFFF...  so is the only addressing space available on
my Mac from 0x200000 to 0xFFFFFF = 14MB (I have one NuBus card)?
Further, how should this affect *virtual* addressing anyway, that
faults to pages in a backing store (i.e.  swap area) on the disc?  All
of this sounds like hardware limitations to addressing _real_ memory
to me, not limitations on virtual addressing.

My IIcx has the same damn HARDWARE as the IIci in terms of the
integrated PMMU in the '030. Why is it not possible for Apple to offer a
ROM upgrade to the IIcx that supports Clean, full 32-bit Memory
managment? I would appreciate a clear answer to this from someone that
knows... Don't worry about getting too technical.


Dave Waller  \  The opinions expressed are solely my own, and in no way
Hewlett-Packard Co.  \  represent those of my employer (but we all know
dave@hpdstma.ptp.hp.com | hplabs!hpdstma!dave  \  they should!)