Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.unix.i386
Subject: Re: SCSI and 386/ix
Summary: An obscene trick is needed....
Message-ID: <1630@aber-cs.UUCP>
Date: 9 Feb 90 21:08:21 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 25

In article <1535@redsox.bsw.com> campbell@redsox.UUCP (Larry Campbell) writes:
    In article <PCG.90Feb5190711@rupert.cs.aber.ac.uk> pcg@rupert.cs.aber.ac.uk (Piercarlo Grandi) writes:
    -Are there really any RLL or MFM controllers (the WD1006 is by
    -your implication) that can step independently the two arms?
    
    Not exactly, but:  most RLL/MFM drives are "buffered seek" drives.  This
    means that the step pulses do not have to be issued at a rate that matches
    the physical movement of the head, but can be issued all at once (50 usec
    apart, I seem to recall);  the drive counts them and then steps the heads
    itself.  So I think you could fake overlapped seeks with such a drive.

Well, I have received by mail some information on how ISC does
it. It is not just the buffering, which may well be there, but
the problem of how do you know that the seek has actually been
completed. This requires a trick. If you look back at a posting
by an ISC guy in this thread the hint is there. It is really
morbid overall, but does work (except on some 1006 controllers).

What worries me quite a bit is news I have read in a recent 'Byte'
issue that the WD1003 programmatic interface has been made into
a standard, and given a suitably horrid acronym. Bah!
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk