trewitt@cascade.Stanford.EDU (Glenn Trewitt) (01/14/89)
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
{ucbvax,decvax}!decwrl!miasma.stanford.edu!trewitt USENet
trewitt@miasma.stanford.edu Internetkaufman@polya.Stanford.EDU (Marc T. Kaufman) (01/15/89)
In article <1250@cascade.Stanford.EDU> trewitt@cascade.ARPA (Glenn Trewitt) writes: >There are some problems that Connectix freely admits: >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). My reading of this would lead me to the conclusion that non-disk SCSI devices would also not work. This includes the Tape Backup 40SC, the LaserWriter SC, Mirus FilmPrinter, etc. Also, disk initialization (formatting and partition building) may fail. I would appreciate hearing more from people who know how the I/O is "REALLY" handled. Marc Kaufman (kaufman@polya.stanford.edu)
ephraim@think.COM (Ephraim Vishniac) (01/16/89)
In article <1250@cascade.Stanford.EDU> trewitt@cascade.ARPA (Glenn Trewitt) writes: >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. >There are some problems that Connectix freely admits: >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). I think this answers an earlier article's question about, "What if a SCSI transfer page-faults?" (Or words to that effect.) It sounds like Virtual hooks the I/O calls and examines the length and address for transfers to be sure that they're paged in. Besides the problem mentioned with scanners, this could also be a problem for SCSI disk formatters, which might issue SCSI commands directly in the course of installing the driver. (SCSI Evaluator is another problem if you select certain options.) I hope Virtual's instructions are quite clear about possible gotcha's and how to debug them. Ephraim Vishniac ephraim@think.com Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214 "Arlo Guthrie, it seems, has found what he was looking for: God, and the Macintosh." (Boston Globe)
kehr@felix.UUCP (Shirley Kehr) (01/17/89)
In article <35421@think.UUCP> ephraim@think.com (Ephraim Vishniac) writes: >In article <1250@cascade.Stanford.EDU> trewitt@cascade.ARPA (Glenn Trewitt) writes: <>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. I called Connectix yesterday asking if we can buy at the show price of $495 even if we aren't at the show. They will accept a major credit card number over the phone or send it COD. The price goes back up to $695 next week (after Sunday 22nd). The sales rep cautioned that the init for 68030-based machines is different from that for the PMMU they are supplying for Mac II. She said that Apple only implemented a subset of the instruction set on the PMMU that comes with the 030 machines. (I barely know what I'm talking about; please forgive the vagueness) <>There are some problems that Connectix freely admits: <>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). <I think this answers an earlier article's question about, "What if a <SCSI transfer page-faults?" (Or words to that effect.) It sounds <like Virtual hooks the I/O calls and examines the length and address <for transfers to be sure that they're paged in. I also asked about the Apple Tape drive, CMS disk drives, and big screens. She didn't have the list of equipment tested by beta sites, but knew one of them has the E-Machines (yea!). She said she uses a tape drive (MacPeaks? - is there a drive like this?) <Besides the problem mentioned with scanners, this could also be a <problem for SCSI disk formatters, which might issue SCSI commands <directly in the course of installing the driver. (SCSI Evaluator is <another problem if you select certain options.) I hope Virtual's <instructions are quite clear about possible gotcha's and how to debug <them. I hope so too, because my boss is very interested in letting me try it. Now, if he can just get HIS boss to say OK in time...(report at 11, if so). Another question I had concerns future OS development by Apple. She had recently attended a talk by Scully who said that multi-tasking and virtual memory were two years away for the Mac. She had also heard that System 7.0 features were to be folded into System 8.0 and that System 7.0 would not be released. (That was not part of Scully's talk. She noted that it was from the rumor columns.) Shirley Kehr