Why would drive run at UDMA33? (Segate 80GB)

Jonathan Arnold jdarnold at buddydog.org
Fri Feb 13 13:41:09 PST 2004

JJB wrote:
>> This is not true. With today's computers, all disks will operate at
>> their highest speed, not matter what other device they are paired
>> with.
>> Their transfer rate may be slowed down if *both* devices are
>> accessed at
>> the exact same time, but that's nothing to worry about generally. So
>> just
>> because you have a CD-ROM and an UDMA100 disk on the same channel,
>> it doesn't mean the UDMA100 disk will be slowed in nearly any
>> noticable
>> fashion.
> I have an PC with mfg date of 5/2003 and the motherboard manually
> has warning note about separating the cdrom drive to the secondary
> IDE controller because it will force the IDE controller to step down
> the max speed to the slowest device. This was not only for cdrom
> drives but also mixing UDMA100 and UDMA66 and UDMA33 disk on any IDE
> controller. IDE max controller speed is set by bios at boot time
> after the probe post process completes. So just exactly what time
> period are you referencing by "With today's computers"?  DO you work
> for Bios chip manufacture, or write the FBSD bios's boot probe code?
> What is your technical background to make such an authoritative
> statement in light of so much information to the contrary?

All you need to do is to Google for "hard drive cd-rom myth" and
you'll get plenty of places that explain this.  I guarantee you
that a UDMA100 drive won't be set at PIO4 just because there's
a CD-ROM drive on the same channel. Your manual is probably talking
about exactly what I said - if both devices are accessed at the same
time, the transfer will occur at the slower rate. But that does not
mean either the bios or FreeBSD doesn't know that a UDMA100 drive
is out there. In fact, my FreeBSD has both a UDMA66 and 100 on it,
and FreeBSD knows all about the two. And if you are just getting
stuff from the hard drive (which is probably 95+% of the time),
then you have a perfectly functioning UDMA100 drive.

> second device to the ribbon. Now if the devices are jumper as master
> and slave it does make an difference which of the 2 closely spaced
> nipples are used as the nipples have default meanings. And I believe

I don't think this is true either. I've hooked up a lot of drives
in my time, and I've never seen this. And no "build it yourself"
guide that I was able to find on the 'net mentioned anything at all
about which nipple to plug into the slave or master drive.

Jonathan Arnold     (mailto:jdarnold at buddydog.org)
Daemon Dancing in the Dark, a FreeBSD weblog:

More information about the freebsd-questions mailing list