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From: del@pilchuck.UUCP (Erik )
Newsgroups: net.micro.pc,net.micro
Subject: AT hard disk speed: explanation.
Message-ID: <346@pilchuck.UUCP>
Date: Tue, 20-May-86 19:35:38 EDT
Article-I.D.: pilchuck.346
Posted: Tue May 20 19:35:38 1986
Date-Received: Sat, 24-May-86 04:55:42 EDT
Organization: Data I/O Corp., Redmond, WA
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Keywords: Why does it go so fast?
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I have lost the original message (our news gets purged SO fast around here),
but this is in response to a posted question about why AT disk operations
benchmarked so FAST.

1) As stated in the article, the AT hard disks seek at least twice as
   fast as the XT hard disks.

2) The XT disk format uses a sector interleave of 6, while the AT uses
   a sector interleave of 2. This means an XT has to wait for 6 full
   disk revolutions to get a full track, while an AT gets it in 2.

3) The AT is just a faster processor (no kidding :-), so time between
   disk accesses is less, too.

I don't know what mathematical algorithm relates the above parameters,
but when you combine them, you do see a speedup of 6-10 times that of
an XT.

Speaking of mathematical relationships, one that I don't understand is
why the disk access (copy to nul for example) is that fast, and Norton
sysinfo says my 9Mhz AT cranks along at 8.7 * PC performance, but my
compiles only go 4-5 times as fast.

I'll just have to live with it, at least till I can buy a 386 machine.