On Sun, May 06, 2001 at 08:15:31PM -0400, abrahams@acm.org wrote:
Philipp Thomas wrote:
* Paul Abrahams [Sun, 06 May 2001 10:20:38 -0400]:
My hard drive claims to be ATA100; the motherboard claims UDMA 33/66 IDE. I'll admit that I know nothing of the relationship between ATA and UDMA, but I had assumed that the numbers were comparable, especially since most hard drives seem to be ATA66. Can you enlighten me?
Yes, they're used interchangeably. BTW, what hard drive is it exactly? But just try to run 'hdparm -tT /dev/<your disk>' (and please post the output :). If you get Numbers below 66 MB/sec (and *no* currently available hard disk even comes near that), it won't get any faster when connected to a ATA100 controller.
Well, there are two numbers, one above 66MB/sec and one below:
root@suillus:/aux/home/pwa > hdparm -tT /dev/hda
/dev/hda: Timing buffer-cache reads: 128 MB in 1.10 seconds =116.36 MB/sec
You won't improve much on this. Normal PCI is 32-bit, 33 MHz. As they say, 'you do the maths'. Unless things have moved on and we actually have 66 MHz PCI machines around? Does anyone know about this? Of course, the moment you plug in a 33 MHz card, the whole bus will slow down to 33 MHz anyway, so even if there are 66 MHz machines around, they'll probably be slowed down by one or more of the cards plugged in to them.
Timing buffered disk reads: 64 MB in 2.03 seconds = 31.53 MB/sec
Limited by the physical disk itself; again, you won't improve on this much. You'll get a slightly lower latency because the data can come down the 100 MHz ATA bus faster, but compared to the latency of the drive, the bus latency is peanuts.
I'll see what happens when I attach the controller.
So if you've bought the controller for higher speed, you've wasted your money. But at least you've now got two more ATA channels, so you can run four ATA devices as master on their own channel. Running ATA devices as master on their own channel is always the best way to attach them as that will give you the most speed when talking to them in parallel (like installing from CD) and will avoid trouble.
That's good to know.
Paul
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