Path: utzoo!attcan!uunet!husc6!think!ames!lll-lcc!unisoft!hoptoad!xanth!kahn
From: kahn@xanth.cs.odu.edu (Gary I Kahn)
Newsgroups: comp.sys.ibm.pc
Subject: Re: programs that run faster at 4.77 Mhz than at 10
Summary: turbo clones often slow for disk access
Message-ID: <5204@xanth.cs.odu.edu>
Date: 10 May 88 22:32:31 GMT
References: <23988@ucbvax.BERKELEY.EDU>
Organization: Old Dominion University, Norfolk Va.
Lines: 13


Any disk access on a turbo PC clone probably slows the processor speed to
4.77MHz.  This is because the floppy drive can't be accessed at, say, 8 MHz if
it is IBM compatible.  As a result, on my clone, every interrupt 13
(disk access) is grabbed before execution, and a short program is run to slow
the clock speed.  After the disk access is completed, the same program
has to execute more code to speed things back up.  This means that a 8MHz
clone might execute a disk-intensive program slower than a standard 4.77MHz
machine.  If the computer is running at the slower speed, the excess code isn't
needed on each interrupt 13.

I've noticed that the CORE test suite shows lower throughput on my hard disk
controller if I'm running at turbo speed than at standard speed.