Path: utzoo!attcan!uunet!cs.dal.ca!lane
From: lane@cs.dal.ca (John Wright/Dr. Pat Lane)
Newsgroups: comp.sys.ibm.pc
Subject: Questions about 1:1 HD controllers (on an XT?)
Message-ID: <1990Apr10.095716.1689@cs.dal.ca>
Date: 10 Apr 90 09:57:16 GMT
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Lines: 49

Some questions about 1:1 controllers.  I understand about hard disk
interleaving and how the optimal interleave factor depends on the
disk drive electronics, controller, and the machine they are operating
in.  The preponderance of controllers that advertise being "1:1 capable"
seems to suggest that it's only the controller that determines the optimal
interleave and that a "1:1 controller" will achieve 1:1 optimality in
any machine with any drive.  Is that so?

On the subject of which components affect optimum interleave factor,
I would suppose that drives are standardized enough that there tends
not to be a significant difference with respect to interleaving.  On
the machine side, CPU speed seems not to make a difference: I would 
suppose that this is because hard disk I/O is handled through DMA and
that bus speed and the DMA electronics were the big factors here.  Am
I correct on these points?

I've always assumed that 1:1 interleaving was possible (both to format
a drive and to read it) on any drive/controller/machine combination; just 
that if any of them were too slow, 1:1 would be a (very) sub-optimal
interleave factor.

So I wonder if these controllers advertised as 1:1 can deliver 1:1 as the 
optimal interleave in *any* machine with *any* drive?

What started this off was a DTK XT controller that was supposedly 1:1.
(Curses! I don't have the model no. but it was also an RLL controller).
It was in a 12-MHz XT with a 30 Meg RLL drive (Miniscribe, I think) that
was, in fact, interleaved at 1:1 according to two programs I have that
test such things.  However, both pgms suggested 1:4 was the optimal 
interleave and so it certainly seemed to be.

A Western Digital tech guy said they did not make a 1:1 controller for
XT's and doubted that it was possible.

So, I'm ultimately wondering if DTK (or anyone else) really does make a
1:1 XT controller, if so, does it really work in all machines, and, if so,
why did 1:1 appear to be sub-optimal in the machine I saw.

Thanks very much for any enlightenment on this subject and, please, if you
post a response, please mail me a copy as I'll likely miss it on the news.
(This site only keeps things for a day or two and I just can't log in that
often! :-( ).  Thank's again.


-- 
John Wright      //////////////////     Phone:  902-424-3805  or  902-424-6527
Post: c/o Dr Pat Lane, Biology Dept, Dalhousie U, Halifax N.S., CANADA B3H-4H8 
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