On Tue, 24 Jun 2014 05:36:48 -0700 (PDT), wrote:

While building some workstations with Centos operating system,
I found some Deskstar 320 GB PATA disks that were hardly used (about 30 hours).
I used these for swap and tmp, although swap shouldn't be used, as there is
heaps of RAM. I used SATA disks for root and home.
Now I find this Deskstar is very slow on one workstation.
Benchmark gives 4 MB/s read, when it should do about 100.
The Deskstar disk is 7200 RPM and supports UDMA6. The mainboard uses a Jmicron
chip for PATA, which also supports UDMA6. It is connected with
80-conductors cable. I swapped the Deskstar drive and the cable, and slowness
seems to be in the mainboard.
RHEL generic IDE driver is claimed to support the JMB368 since version 4.6,
and I have version 5.10.
hdparm shows the drive is running in UDMA5, which is ATA100 instead of
maximum ATA133, but is way faster than 4 MB/s
The SMART data shows no problems with the drives.

quite a few ideas to pursue for resetting UDMA in the Wenviron, a
few(er) hardware centric
http://winhlp.com/node/10