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

JJB Barbish3 at adelphia.net
Fri Feb 13 08:31:18 PST 2004

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?

Now on the subject of which end of the IDE ribbon you plug into the
motherboard. I agree with you that it makes no difference other that
one end has 2 nipples closely spaced together and if that end is
plugged into the motherboard it's next to imposable to attach an
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
the default nipple meaning (IE: master, slave) changed from the
UDMA33 of the ending nipple being master to middle nipple being
master for UDMA66 & 100.  Now I am no technical wizard, but that has
been me experience as new PCs have replaced older ones in the
company I work for and I have had to configure them before giving
them to the users. Now the work PC all rum ms/windows and I can see
the 'post' summary display shows the UDMA of 33 on both devices when
I have an UDMA100 hard drive and UDMA33 cdrom on same IDE
controller. The hard facts just do not match you generic statement.

-----Original Message-----
From: owner-freebsd-questions at freebsd.org
[mailto:owner-freebsd-questions at freebsd.org]On Behalf Of Jonathan
Sent: Friday, February 13, 2004 9:59 AM
To: freebsd-questions at FreeBSD.ORG
Subject: Re: Why would drive run at UDMA33? (Segate 80GB)

(Still going through some old messages, but this thread had some
misconceptions and myths that I'd like to straighten out):

> ATA channel 0:
>     Master:  ad0 <ST380021A/3.19> ATA/ATAPI rev 5
>     Slave:  acd0 <CD-RW 24X10X40/Y.IW> ATA/ATAPI rev 0
> ATA channel 1:
>     Master:  ad2 <ST380011A/3.06> ATA/ATAPI rev 6
>     Slave:       no device present
> Here is your problem. On channel  0  You have an UDMA100 disk and
> UDMA33 cd-rw. The motherboard IDE controller steps down the speed
> the speed of the slowest device. You have to move the cd-rw device

This is not true. With today's computers, all disks will operate at
their highest speed, not matter what other device they are paired
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
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

Also mentioned in this thread was something about the cable being
connected "backwards". There is no "motherboard" and "disk"
direction in an IDE cable, be it a reguler one or a UDMA 100 one.
are made to be a little more convenient if you hook them up the
way (with two connectors closer together at one end), but it has no
bearing on the speed or the UDMA detected.

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