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From: rpd@apple.UUCP (Rick Daley)
Newsgroups: comp.sys.mac
Subject: Re: A/UX filesystem performance
Message-ID: <1353@apple.UUCP>
Date: Thu, 23-Jul-87 02:28:39 EDT
Article-I.D.: apple.1353
Posted: Thu Jul 23 02:28:39 1987
Date-Received: Sat, 25-Jul-87 05:43:21 EDT
References: <44025@beno.seismo.CSS.GOV> <10252@amdahl.amdahl.com> <2495@hoptoad.uucp>
Organization: Apple Computer, Inc., Cupertino, USA
Lines: 31
Summary: A/UX does NOT run on top of the Mac OS!

In article <2495@hoptoad.uucp>, tim@hoptoad.uucp (Tim Maroney) writes:
> A/UX runs on top of the Mac OS.  If the UNIX file system is not "real UNIX"
> but merely a front-end to the Mac HFS software, then the single-threaded
> nature of HFS could be expecvted to present extreme performance obstacles,
> since only one process's file system request can get serviced at once, and
> the rest are sleeping.

NO! NO! NO!  A/UX does NOT run on top of the Mac OS.  It is a "real UNIX"
and uses a "real UNIX" file system.  A/UX is based on System V.2 with
extensions from V.3 and BSD 4.[23].  The file system is System V.  Performance
problems in the A/UX file system stem from three problems:
    1) The software needs tuning.  A/UX is still pre-release and we have been
more concerned with completeness and robustness than tuning.  We have been
doing work in that area, but none of the beta sites have seen the results.
    2) The file system is System V style, not the Berkely "fast file system."
I, for one, hope that the fast file system will be an option in future
releases of A/UX, but it will not be so for the first release.  The fast file
system yields better performance and supports long file names.
    3) The Mac II does not have any DMA hardware.  This does not hurt the
native Mac OS too badly as long as only one process is really active at a
time.  It is very rare for a Mac program to do anything during a read but wait
for the read to complete.  Therefore, it doesn't matter if the CPU has to
move the bytes itself.  This lack of DMA hardware means that disk I/O will
always be a weak point of A/UX performance on a Mac II.

Since I spend my days (and nights) working on the A/UX Toolbox, I'd like to
think Tim got confused when he saw a demo of A/UX looking and feeling like a
Macintosh.  However, this is the Macintosh Toolbox running on top of A/UX,
not the other way around.
						Rick Daley
						rpd@apple