Mike Hardy wrote:

That's more like what we were expecting!

I can't tell you why its like that or how, but this *is* the typical
problem with IDE. Most likely the chipset is being detected incorrectly,
or its being detected correctly but there is some errata that's
disabling dma, or maybe dma is experimental for the card.

Places to look for information are in the dmesg for the sis chipset's
detection diagnostics, then on the internet as a google for your sis
chipset number then "linux dma" maybe. You may end up with some ide
things on your kernel command line (via grub or lilo)

I'll reiterate something I said previously though, other than
write-caching (which is potentially dangerous) none of the other hdparm
or IDE settings are really going to give you that much of a boost unless
your workload is specifically tunable. They're all just little minor
twiddles you can do - nothing even close to the difference between
having DMA or not. So I'd just focus on enabling DMA. The other stuff is
all uninteresting compared to it.

-Mike

Thanks for the reply Mike.  After some Googling and looking at my kernel 
config file,  it seems that SIS support is a module, like so:

CONFIG_BLK_DEV_SIS5513=m

I found this link but can't find any of the files that it references

http://kerneltrap.org/comment/reply/4925/129324

I'm not sure if having CONFIG_BLK_DEV_SIS5513 as a module has anything 
to do with this.

I can't get to my box right now, because out of curiosity I did hdparm 
-D 0 /dev/hda and ran the dd test, I think it crashed the box.  The box 
is in my basement at home, so I'll have to wait until tonight.

Jay