From: pcg@aber.ac.uk (Piercarlo Grandi)
Newsgroups: comp.arch
Subject: Re: OS/MFT and Macintosh (was: ..History)
Date: 5 Sep 92 13:22:52 GMT
Reply-To: pcg@aber.ac.uk (Piercarlo Grandi)
Organization: Prifysgol Cymru, Aberystwyth

On 3 Sep 92 14:44:36 GMT, johnl@iecc.cambridge.ma.us (John R. Levine) said:

smith> OS/MFT provided a "flat" file system.

pcg> Really? That's news.

johnl> It's true, mostly. [ ... VTOC was just a flat table of file
johnl> names, somewhat like the ilist under Unix ... ] The catalog, on
johnl> the other hand, was indeed tree structured [ ... ] But it
johnl> appears that in most installations, people were very sloppy about
johnl> using the catalog [ ... ] and there were a lot of strange flat
johnl> names.

Well know, unfortunately. A possible reason for Smith's mistake.

johnl> PS:  Followups to comp.arch.history, if it ever exists.

Actually there is something more architecturally relevant to be said.

Making a comparison between a microprocessor OS os the eighties with one
of a mainframe in the sixties has to be taken with a wide margin of
imprecision. Smith's nitpicking remark that MacOS is more like MVT than
MFT looks rather silly in this respect; I could even defend the notion
that MacOS is actually more like MFT than MVT, by pointing at some
particular features in MVT that are not yet in MacOS.

Actually it can be argued that MacOS (in its three incarnations, without
multifinder, with multifinder, with single address space VM) is under
certain respects more like the original PCP.  While MVT had a variable
number of partitions, and MFT had a fixed number, they also had a lot of
things, like tasks, memory protection, scheduling, volume management,
generalized locking, that are yet to be seen in MacOS.

But the main gist of my observation was that, broadly, in the various
architectural generations that operating system design has gone through
(very roughly: none in the 40s, single program loaders in the 50s,
multiple programs in the 60s, timesharing in the 70s, modularized in the
80s), MacOS belongs to the same generation as OS/360 or 370, in its
various incarnations as PCP (first few releases of MacOS), MFT/MVT
(MacOS 6) or SVS (MacOS 7).

Indeed, as another poster observed, the original MacOS, and even today's
MSDOS, was much more like the original OS/PCP, or maybe, let me say,
more like the 7090 monitor/program loader.

One sad thing about all this is that the machines on which MacOS and
MSDOS run are some orders of magnitude more powerful and sophisticated,
under many respects, than those on which PCP/MFT/MVT/SVS used to run.
Hey, the GE645 used to develop Multics did not have the power required
today to run Windows 3 or MacOS 7! And the original Xerox Alto or Star,
which had far neater GUIs than the Windows or MacOS ones, could not
possibly run either!

Another one is that not only most major microprocessor operating systems
are still stuck with technology of the sixties, but also with the least
agreeable sixties technology. I mean, in the sixties one had CTSS, for
example, which is still more advanced then either MacOS or MSDOS, and
its successor, Multics, which is still far more advanced than things
like OS/2 or "Unix" (e.g. in its 4.3BSD/SVR4/SunOS incarnations -- Mach
is another thing really).

I could even go as far as saying that most/a lot of the technology in
currently popular OS architectures can be directly traced back to the
fifties (my favourite example is 'ld' on many "Unix" implementations).

All this is not encouraging. I seem to have noticed that as the computer
market has expanded, the lead time for new technology has increased. I
think that as things currently are, the time between successful
demonstration of an architectural technology and its diffusion in the
marketplace now stands at around 20 years (for example Accent,
reincarnated as Mach3, was conceived about 15 years ago, and its
underlying technology is only now becoming popular), if ever.

This surely has (dire) implications for architecture in all branches of
computer science.
--
Piercarlo Grandi                   | JNET: pcg@uk.ac.aber
Dept of CS, University of Wales    | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@aber.ac.uk
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