Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!apple!oliveb!tymix!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga
Subject: Re: Why do you need metaphor? (Re: What should be learned
Summary: Multi-megabyte files should be easy to create
Message-ID: <549@tardis.Tymnet.COM>
Date: 1 Sep 89 21:08:11 GMT
References: <22976@louie.udel.EDU>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: McDonnell Douglas Field Service Co, San Jose CA
Lines: 35

In article <22976@louie.udel.EDU> Ata@multics.radc.af.mil (John G. Ata) writes:
>    From:  Kent Paul Dolan <xanthian at WELL.UUCP>
>    improve the world.  The Unix file as a stream of bytes paradigm made a
>    horrendously complicated process in every other file system much easier
>    to comprehend.  And no, that god-awful segmented mess that was Multics
>    idea of a file doesn't begin to compare.
>
>Indeed!  Perhaps you would like to make a comparison?  I suspect that
>although your knowlege of Unix is present, your understanding of the
>Multics system is not all that deep.  Please note that the segmentation
>and paging on Multics, as well as the file structure in a stream file,
>is invisible to the programmer where a segment to most programmers is
    ^^^^^^^^^
>merely a file.

From my short experience with Multics, the segments were NOT invisible.
Each segment was limited to 256K words (36 bit words, 18 bit addresses).
The instant you tried to make a sequential file bigger than 256K words (1
megabyte), segments became PAINFULLY obvious.  You had to stop what you were
doing, create an empty multi-segment file (which acted sort-of like a
subdirectory), copy half of your input file to one segment, half to the
other, delete the original, rename the new file, and then try to continue as
if nothing had happened.  Small files were wonderful, large files were not.

Maybe they fixed it after I stopped using Multics, but I agree with
Kent; large files on Multics were a god-awful segmented mess.

The ability to map a file into your virtual address space is great, provided
that the OS and/or CPU is not hobbled with a too-small limit on ranges of
virtual addresses.
-- 
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