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Date:      Fri, 29 May 1998 08:41:58 +0930
From:      Greg Lehey <grog@lemis.com>
To:        chat@FreeBSD.ORG
Subject:   Re: Compatibility with Ultra IDE drives?
Message-ID:  <19980529084158.B25469@freebie.lemis.com>
In-Reply-To: <19980528214824.A12555@keltia.freenix.fr>; from Ollivier Robert on Thu, May 28, 1998 at 09:48:24PM %2B0200
References:  <19980528102719.D342@freebie.lemis.com> <Pine.BSF.3.96.980528110226.2373R-100000@gdi.uoregon.edu> <19980528214824.A12555@keltia.freenix.fr>

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On Thu, 28 May 1998 at 21:48:24 +0200, Ollivier Robert wrote:
> According to Doug White:
>> Hm, I'll have to demo a UltraDMA computer.  I'm only on standard IDE.  Is
>> UltraDMA tothe point where it actually is a win?  Originally the critics
>> were saying there was no win with ultradma.
>
> The main difference is PIO vs DMA. UltraDMA should not make any real
> difference because no disk is able to push that much data out...
>
> You can get 11 or 12 MB/s from a modern drive (maybe a bit more with 10k
> rpms but they're not available to IDE) so having an IDE interface at 33
> MB/s is useless IMO.

I think you're being a little hasty here.  Sure, 33 MB/s is much more
than is needed at the moment, but what will things look like in 6
months?

In this connection, I noticed a significant difference just now on two
different machines, one a K6/233 with Ultra DMA, the other a P5/133
with PIO.  Both were running an IBM DHEA 36480 6.4 GB IDE drive.
Here are the results:


Transfer     Transfer	Interrupt	CPU
mode	     speed	time		idle
	     (MB/s)	(%)		(%)

DMA	     10.3	1.2		91.9
PIO	     2.4	95.3		0.0

The PIO machine was effectively frozen during this time.  This is
probably the effect to which Doug White was referring.

The difference between the CPUs doesn't make a significant difference
for the DMA transfer.  If the PIO test had been done with the K6, I
would expect to still see 100% busy, but I'd expect a faster transfer
rate (maybe 6 MB/s).
Greg
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