Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pacbell!belltec!jim
From: jim@belltec.UUCP (Mr. Jim's Own Logon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What is the fastest disk access method on AT?
Summary: Doesn't apply...
Message-ID: <295@belltec.UUCP>
Date: 28 Oct 88 13:32:58 GMT
References: <211@focsys.UUCP> <10480@cup.portal.com>
Organization: Bell Technologies, Fremont, CA
Lines: 21

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).


   But almost all hard disk controllers are string I/O based, and are not 
based on the DMA controller at all. I say almost all because someone,
somewhere must have one that does (probably made before everyone found
out how slow they were).

By the way, I hate how the usage of 'DMA' now seems to automatically
refer to the usage of a DMA controller. Only in the PC realm of the
world is multimaster support so weak that using the DMA chip is easier
than implimenting a true DMA from an alternate bus master.

						-Jim Wall
						Bell Technologies, Inc.