Let me explain this better. I have a old computer and a new one that im building. The old computer has a Maxtor 40gig diamond plus 8 ATA in it with a motherboard that supports ATA 33/66/100. My new computer will have a motherboard that supports ATA 33/66/100/133. I cant figure out if I should (or can) just take the old hard drive out and put it on my new PC for now and buy a ATA 100 hard drive for the old computer (my kids will use the old computer when im done) or should I buy a new ATA 133 for my new computer. Or does it matter if I buy a Seagate 100 for my new motherboard(supports 33/66/100/133) or can I even use a ATA 150 for my new motherboard even though it doesnt support ATA 150. Im lost. I think I might be looking at this whole ATA concept wrong. I mean doesnt the higher ATA mean the faster the Hard drive? I dont know what too do....