Using the CD version of Knoppix 4.02, hdparm -t /dev/hda shows that my
drive is only working at 4 MB per second. Under Knoppix 3.6 and Fedora Linux,
hdparm reports 60 to 62 MB/second.

hdparm -t /dev/sda shows that my USB memory key is 1 MB/second, but
it runs at 8 MB/second under Knoppix 3.6 or Fedora.

hdparm -I /dev/hda reports exactly the same information under Knoppix 4.02,
Knoppix 3.6, and Fedora. Specifically, they both show that my ATA 100 drive is
definitely using the UDMA5 mode.

The slowdown is real, not a quirk of hdparm. I use this dd command to back up my system.
dd if=/dev/hda1 of=/dev/hdc1 bs=2M
Under Knoppix 4.02, the backup takes unbearably long. Under Knoppix 3.6 the drive to drive
copying is done at more than 50 megabytes per second.

My hard drives are identical ATA 100 Seagate Barracudas. My motherboard is a GA=7N400,
which has the nForce2 chipset.