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From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.minix
Subject: Re: at_wini patches for 6 and 8 mhz PC-AT
Message-ID: <3026@ast.cs.vu.nl>
Date: 20 Aug 89 14:23:25 GMT
References: <21763@louie.udel.EDU>
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Organization: VU Informatica, Amsterdam
Lines: 22

In article <21763@louie.udel.EDU> Leisner.Henr@xerox.com (Marty) writes:
>Enclosed are diffs so the 1.3b winchester driver will run successfully on
>both 6 and 8 Mhz ATs.  I haven't tried this on any other machines yet, but
>I know from experience the AT driver is a problem.  

The at_wini.c driver is unfortunately very fragile.  I didn't write it, and
the student who did, has long vanished.  I am very hesitant to tinker with
it any more, since any change may break machines where it did work.  If the
net can collectively come up with a version that is better than the current
one in the sense of working on more machines, I'm certainly interested, but
it has to be thoroughly tested.

On the subject of disk performance, the single-threadedness of MINIX was
mentioned, but that is irrelevant, as MS-DOS is also single threaded.  It
is my suspicion that the performance loss is mostly due to a poor choice
of interleaving.  The drivers actually have a provision for software
interleaving.  Maybe somebody could experiment with it.  Another interesting
test is a large number of random reads to see how MINIX does against
MS-DOS.  If the blocks read are not consecutive, but randomly strewn over
the disk surface, interleaving won't be an issue.

Andy Tanenbaum (ast@cs.vu.nl)