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Date: Mon, 19 Mar 2001 14:33:41 -0500
From: Jeremy Jackson <jerj@coplanar.net>
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To: Tim Moore <timothymoore@bigfoot.com>
CC: linux-kernel@vger.kernel.org
Subject: Re: UDMA 100 / PIIX4 question
In-Reply-To: <20010318165246Z131240-406+1417@vger.kernel.org> <3AB65C51.3DF150E5@bigfoot.com>
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Tim Moore wrote:

> quintaq@yahoo.co.uk wrote:
> > I have an IBM DTLA 307030 (ATA 100 / UDMA 5) on an 815e board (Asus CUSL2), which has a PIIX4 controller.
> > ...
> > My problem is that (according to hdparm -t), I never get a better transfer rate than approximately 15.8 Mb/sec.  I achieve this when DMA is enabled, - without it I fall back to about 5 Mb /sec.  No amount of fiddling with other hdparm settings makes any difference.
> > ...
>
> 15MB/s for hdparm is about right.

Yes, since hdparm -t measures *SUSTAINED* transfers... the actual "head rate" of data reads from
disk surface.  Only if you read *only* data that is alread in harddrive's cache will you get a speed
close to the UDMA mode of the drive/controller.  The cache is around 1Mbyte, so for a split-second
re-read of some data....

>
>
> "...four IDE devices can be supported in Bus Master mode.
>  PIIX4 contains support for "Ultra DMA/33" synchronous DMA
>  compatible devices."
>
> http://developer.intel.com/design/intarch/techinfo/440BX/PIIX4_intro.htm
>
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