🚀 go-pugleaf

   From: bparsia@eagle.wesleyan.edu
   Newsgroups: comp.sys.mac
   Date: 3 May 90 17:50:11 GMT
   Distribution: usa

   In article <8904@hydra.gatech.EDU>, gt4586c@prism.gatech.EDU (WILLETT,THOMAS CARTER) writes:

    [stuff deleted...]

	   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.

Not entirely true.  System 7.0's virtual memory will have the same
limitation ("14-1 per slot") as Virtual unless you have 32-bit clean
ROMs (standard on the IIci & IIfx).  The 32-bit clean ROMs will work
in the IIcx, but you'll have to buy and install them (they come on a
SIMM, but I know nothing about their where to buy them).

	   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.

True.

	   However, I'm confused. I thought that the Mac OS currently
   supports *only* 8 megs of memory. Does Virtual patch this in some
   manner?

The limitation is that the ROM is expected to be at address 800000 hex
(8 Megs).  Virtual fools the finder into thinking that there is an
application sitting in memory where the ROM is (or something like
that).  Thus your virtual address space is split up into an 8 Meg
chunk and a "6 meg - 1 meg per filled NuBus slot" chunk.

	   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).

And the Mac will be able to thrash almost like a real operating
system.

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

No hardware differences, just the 32-bit clean ROMs.

   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?

   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).

I work for Apple, but I'm no official, so I include the standard
disclaimer that all my musings are my own opinions, not my employer's.

Bill St. Clair
bill@cambridge.apple.com