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From: gst@talcott.UUCP (Gary S. Trujillo)
Newsgroups: net.micro.pc
Subject: Re: hard disk interleave
Message-ID: <572@talcott.UUCP>
Date: Mon, 3-Mar-86 00:13:42 EST
Article-I.D.: talcott.572
Posted: Mon Mar  3 00:13:42 1986
Date-Received: Tue, 4-Mar-86 03:37:43 EST
References: <1480@sdcsvax.UUCP>
Organization: Harvard Univ. Sociology Dept. Cambridge. MA
Lines: 35
Summary: reference to Byte article regarding question on interleave factor

In article <1480@sdcsvax.UUCP>, allyn@sdcsvax.UUCP (Allyn Fratkin) writes:
> I have some questions about disk interleaving.  What is the default
> interleave of the hard disks in IBM PC ATs and XTs?  I have heard that
> the default interleave is much too low, around 2 or 3, and that disk
> performance can be signifigantly increased by reformatting with
> a higher interleave.
> 
> I would really appreciate it if someone could clear this up for me.

The subject of disk interleave factors, as well as other technical
goodies about such things as cluster sizes and encoding techniques
are covered very nicely by Marcus Kolod in his article (p. 283) in
the Fall 1985 issue of Byte in his article entitled "IBM PC Disk
Performance and the Interleave Factor."  (The same issue contains
a couple of additional articles on hard disks on the AT.)

He concludes the article, which contains diagrams and tables showing
the effects of diddling the various things one can diddle when
formatting hard disks, shown both for the XT and the AT, by saying:

	Did IBM choose the best interleave?  There is a discrepancy
	between the stated interleave (6) in the DOS 2.0 manual and
	the interleave that both showed the best times in my test and
	matched the interleave of a brand new XT from IBM, namely, 7.
	Considering that, I think the answer is yes for both machines.
	IBM has optimized its code around single-sector reads.  Although
	DOS may intermittently perform multiple-sector reads, it primarily
	accesses single sectors.

	If multiple-sector reads are performed, it does appear that
	better interleaves exist.

-- 
	Gary Trujillo
	(harvard!talcott!gst)