Path: utzoo!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!bloom-beacon!tut.cis.ohio-state.edu!husc6!linus!philabs!micomvax!ray
From: ray@micomvax.UUCP (Ray Dunn)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What is the fastest disk access method on AT?
Message-ID: <1347@micomvax.UUCP>
Date: 1 Nov 88 20:48:33 GMT
References: <211@focsys.UUCP> <10480@cup.portal.com>
Reply-To: ray@micomvax.UUCP (Ray Dunn)
Organization: Philips Electronics Ltd. (TDS - Montreal) St. Laurent QC, Canada
Lines: 28

In article <10480@cup.portal.com> Devin_E_Ben-Hur@cup.portal.com writes:
>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).

This is completely true, unfortunately it is also completely irrelevant -
the hard disk does *not* use the DMA!!

Speed optimization should be done by using BIOS INT 13 to do your I/O, to
get as close to the hardware as you can without actually "sucking the
ferkin".  You should also match your requests with the physical layout of
the data on the disk, the number of sectors per track, and optimize the
interleave by trial and error.

This is of course a pain in the neck and dreadfully unportable.

If things have got to this sorry state, it is almost certain that you need
to examine very carefully your whole approach to your application
requirements.  Good Luck.

PS - checking the obvious - what is the state of your VERIFY flag?
-- 
Ray Dunn.                      |   UUCP: ..!philabs!micomvax!ray
Philips Electronics Ltd.       |   TEL : (514) 744-8200   Ext: 2347
600 Dr Frederik Philips Blvd   |   FAX : (514) 744-6455
St Laurent. Quebec.  H4M 2S9   |   TLX : 05-824090