Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!portal!cup.portal.com!Devin_E_Ben-Hur
From: Devin_E_Ben-Hur@cup.portal.com
Newsgroups: comp.sys.ibm.pc
Subject: Re: What is the fastest disk access method on AT?
Message-ID: <10480@cup.portal.com>
Date: 25 Oct 88 18:39:25 GMT
Article-I.D.: cup.10480
References: <211@focsys.UUCP>
Organization: The Portal System (TM)
Lines: 12

Larry Williamson asks about improving throughput using int 25&26 disk
IO calls with 64k buffers.

The AT DMA chip can only handle requests that do not span a 64k hardware
memory boundary (that is, the high 4 bits for DMA must remain constant).
If your 64k buffer passed to int 25/26 does span a 64k boundary, the BIOS
function will deblock your request into two DMA controller requests, thus
reducing your thruput. Allocate your disk buffer such that its
address is of the form S000:0000 for some hex digit S.

Devin_Ben-Hur@cup.portal.com    (port-hole-flames > /nev/dull)
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