\_ Well, first test your drive by doing hdparm -Tt /dev/hda (or whatever drive)
\_ and it will give you a transfer benchmark.  Then enable 32 bit transfer and
\_ DMA by typing hdparm -c3d1 /dev/hda .  

This was quite instructive for me....  The most amusement came when I
noticed my aging scsi disk (5+ years) had better performance than the
default hda conf on a 2 month old [commodity] system:

[new] /dev/hda:
 Timing buffer-cache reads:   128 MB in  4.31 seconds = 29.70 MB/sec
 Timing buffered disk reads:  64 MB in 26.50 seconds =  2.42 MB/sec

[aged] /dev/sda:
 Timing buffer-cache reads:   128 MB in  4.26 seconds = 30.05 MB/sec
 Timing buffered disk reads:  64 MB in 18.08 seconds =  3.54 MB/sec

After I got done chortling to myself, I tried the hdparm -c3d1 trick
and lo, the results on part of the test bumped up significantly:

/dev/hda:
 Timing buffer-cache reads:   128 MB in  4.22 seconds = 30.33 MB/sec
 Timing buffered disk reads:  64 MB in  4.43 seconds = 14.45 MB/sec

It's nice to know that technology that's five years newer can make a
difference.  What's sad is that the technology doesn't self enable....

David