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SubjectRe: Can't set UltraDMA mode 2 on Quantum Fireball SE
Don Fisher wrote:

> I have a new maxtor 8.4GB UDMA drive (88400D8) on an ASUS
> TXP4 mothboard. The disk is twice as slow under udma as it
> is under pio. From a fresh boot (so there is nothing in the
> caache I hope) it takes 16 seconds to start emacs under
> udma, and 8 seconds for the same operation using pio. My
> laptop, which also uses pio, also starts in 8 seconds.
>
> Shouldn't udma be faster?

UDMA is exactly the same speed w.r.t. the media.
It won't make a slow drive any faster.

UDMA just halves the tranfer time (a tiny part of the whole
equation) between the drive and the host chipset, improving
things overall by maybe 5-10% in common cases.

If your drive is slower in UDMA mode, then perhaps it has
not been set up for the fastest UDMA timings (BIOS),
so PIO would appear faster.

Given that the drive is a Maxtor (known for their blazing speed),
I'd guess that to be the case. There is no program to check
the UDMA mode at present, though "hdparm -I" might give some
indication (look for a "*" next to mode2 DMA).

>And what is broken for drives greater than 8GB?

The system thinks they are exactly 8GB in size,
even when they're really 12GB (or whatever).
--
mlord@pobox.com
The Linux IDE guy

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