I suppose either will work fine. LOL I have the stock IBM 60 gig on the ATA/100 bus on mine and 2 80 gigs on the ATA/66 bus. Both 8 meg caches, one from Western Digital and the other a Maxtor fluid bearing drive. They've all been fine so far, just one bit of advice. When you do put it in, put the new drive on the ATA/66 bus to equalize the load on both busses. Putting them both on the ATA/100 is nice but will limit the available bandwidth for both drives. Also make sure you plug in the ATA/66 cable to the motherboard, it's not plugged in by default.