Path: utzoo!attcan!uunet!lll-winken!ncis.llnl.gov!helios.ee.lbl.gov!pasteur!agate!bionet!ames!killer!rpp386!dalsqnt!pollux!ti-csl!m2!holland
From: holland@m2.csc.ti.com (Fred Hollander)
Newsgroups: comp.sys.mac
Subject: Re: Virtual memory init
Message-ID: <68267@ti-csl.CSNET>
Date: 26 Jan 89 16:35:46 GMT
References: <1542@csuna.UUCP> <76000334@p.cs.uiuc.edu> <13871@cup.portal.com> <288@berlin.acss.umn.edu>
Sender: news@ti-csl.CSNET
Reply-To: holland@m2.UUCP (Fred Hollander)
Organization: TI Computer Science Center, Dallas
Lines: 40

In article <288@berlin.acss.umn.edu> grg@berlin.acss.umn.edu (George Gonzalez) writes:
>
>I don't understand all the amazement about this virtual memory INIT.
>It would be amazing if it did full-blown virtual memory, with variable
>sized segments, rings of protection, gates, access levels, et. al.

The interest is due to the price difference between the INIT ($695) and an
8Meg memory upgrade ($2400).  Although, it may not be publishable in a journal
of computer science, it is worthy achievement for the Macintosh.

>But if it is to be transparent to the current Mac OS and applications, it
>can't be that fancy.  It sounds like it's just doing *paging* of fixed
>sized blocks between RAM and the disk.  This is less than trivial, but 
>perhaps only 20% of the complexity of full virtual memory.  Not all that
>difficult to do.

Sounds like you could be their first competitor.  And since it will be so
easy, you could sell it for say $50 (software only) and release it in say
a month - you'll certainly put Virtual out of business.  But, don't make the
same mistake they made but fitting into a 10K INIT.  Make yours at least 150K
so that it will be more credible.

>It also does not sound that computer-sciency.  It probably involved more
>trial-and-error experimenting than pure computer science.  I'm sure there
>was a lot of cut-and-try, as the Mac OS's internals are not too well
>documented.  As others have mentioned, there are some tricky areas if
>a page fault occurs during a disk operation!  They probably attacked the
>problem by patching the Mac I/O system, not by referring to Knuth.

Are you sure you're in the right newsgroup.  This is comp.sys.mac.  I agree
that it's no breakthrough in computer science.  Of course it's a patch.  Does
Knuth hack Macintosh!?  I can see it now, The Art of Computer Programming,
Vol 4, Macintosh Internals :)

Fred Hollander
Computer Science Center
Texas Instruments, Inc.
holland%ti-csl@csnet-rela

The above statements are my own and not representative of Texas Instruments.