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From: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Newsgroups: comp.arch
Subject: Re: the Multics from the black lagoon :-)
Message-ID: <5672@blake.acs.washington.edu>
Date: 8 Feb 90 23:30:30 GMT
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In article <1990Feb7.221800.804@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>In article <2093@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
>>UNIX is just
>>beginning to implement some of the ideas which have been working in
>>Multics for two decades, such as mapping files to memory.
>Gee, how could we ever have lived without that for two decades?  :-)
>Maybe because we don't need it and it doesn't buy us very much?

I cannot let this pass without rebuttal.

I could just as well say "Tenex/TOPS-20 lived without pipes and a
powerful shell for 21 years because pipes/shell weren't needed and
they didn't buy very much."  This is perhaps true; TOPS-20 hackers
spent all their time in TECO/EMACS and DDT.  The equivalent of the
"quick shell script" was the "quick DDT program".

I could just as well say "programmers on micros lived without anything
more advanced than DOS and BASIC for years.  C and Unix aren't needed
and don't buy very much."  1/2 :-)

File/memory mapping, or more precisely, the integration of the virtual
memory system and the filesystem, is perhaps one of the most important
and useful features of an operating system which has it.  I am talking
about full-fledged mapping, which you can have muliple read/write maps
of the same file segment across multiple processes.

File management on Unix is horrible.  Anyone who tries to implement a
database (e.g. an electronic mail system) for Unix knows how difficult
it is to do something as simple as a robust and safe file lock.  Let's
not even mention multiple simultaneous file access and interprocess
semaphores.

Many of the algorithms I used in TOPS-20 software had to be replaced
(not just translated from assembly to C) because they were
*unimplementable* in Unix.  In many cases, I had to write complex
scheduling and polling algorithms to replace a simple blocking
algorithm that depended upon file/memory mapping and semaphores.

Now, I may accept the claim that file/memory mapping will be less
useful on Unix, because it won't be standard on every Unix system (and
hence you're forced to write the non-mapping code anyway).  It should
have gone into the first versions of BSD; it's a bit late now.  That
does not mean that it is something that programmers of the future
should have to "live without".  Even Unix will become history some
day.
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