🚀 go-pugleaf

Several people asked about the new product "Virtual" (TM) from
Connectix that provides virtual memory for Macintosh II and other Mac's
with PMMU's.  In this message, I hope to answer some of those questions.

First, a DISCLAIMER:
I am not am employee of Connectix.  I am, however, a friend of the
founders.  I am a beta-test site.  (Can a person be a site?)  Also, I
know internal details about the product, so I AM UNDER NON-DISCLOSURE
in those areas.  Nevertheless, I consider myself a fairly impartial
evaluator.  I am trying to provide information, not advertising.

First, about my beta-test: I have a Mac II with 2 Mb of real memory and
a Jasmine 70-meg drive (24 mSec, I think).  The only times I notice the
presence of Virtual is when it boots up and installs itself (a few
seconds delay) and when changing levels in Tetris (it has to pull a
full-screen 8-bit color image from the disk, which takes about a second
longer than normal because of swapping).  Other than that, I've
forgotten that it's there.  I've also forgotten that I only have 2 Mb
of memory, which is the whole point.  It's very nice and I won't
belabor the obvious benefits of having 8 Mb of memory.

I've been using Virtual for a bit over a week.  I only run "regular"
applications such as HyperCard, MacWrite, Excel, Kermit, etc.  I do NOT
do program development.  In that time, I had one crash when copying a
very large folder with some very large files in it.  I was unable to
duplicate the crash, either with or without Virtual installed.  (Like
most INITs, you can disable its installation by holding down a key
(Escape, in this case) when booting.) My conclusion is that, for normal
applications, it works fine.  Applicable quote: "Before, my Mac crashed
once a day, whether it needed to or not.  Now that I have Virtual, it
still crashes once a day, whether it needs to or not." :-)

There are some problems that Connectix freely admits:

1) Currently, most debuggers will not work with Virtual running.  This
is a known problem, and will be fixed.  Some debuggers are very poorly
behaved and root around in all sorts of nasty places.

2) Virtual does not currently work with software that does direct SCSI
I/O, bypassing the OS file manager (?) calls.  Connectix is working on
this.  Most scanner software does this when actually scanning something
(but not when doing post-processing).

3) Virtual will not work with hardware (i.e.  NUbus boards, especially
coprocessors) that does DMA, because DMA bypasses the PMMU and writes
directly to memory.  With Virtual running, the memory isn't where the
the board expects.  This problem is very difficult to fix and would
require changes to the drivers and the Apple OS.  Don't expect anything
soon.

In all of these cases, Virtual can be turned off by rebooting and these
things will work OK.  For most people who run "plain vanilla"
applications, Virtual should work well.

Some answers to some questions that I saw here earlier:

1) The page size is 2K, and the replacement algorithm is LRU, although
ages are only checked periodically.  This works fine for the Mac, which
doesn't have real multi-tasking.  Most paging will be directly
user-driven -- when the user switches applications under MultiFinder.

2)  As far as I know, single-unit prices on the 68551 PMMU are over $250.

3) MacNosy's debugger functions don't work under Virtual, although its
disassembly functions should (don't know if that's been extensively
tested) work fine.

Finally, there were several misprints in MacWeek and in the BMUG note:
The MacWorld Expo show price is $495 with PMMU; $259 without.
Connectix' phone number was misprinted in MacWeek; the correct one is
(415) 324-0727.  As stated in the article from BMUG, they will have a
booth at MacWorld Expo in Brooks hall, perhaps in Moscone.

-- 
Glenn Trewitt, Center for Integrated Systems, Stanford University
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