I have come to the realization that I need to get an external HD to back up my main HD on my iMac. I am thinking the best bang for the buck is to get an internal Seagate HD and use an external case. My machine will accomodate up to FWire 400 and I am thinking of 250 GB or 320GB. O will use it for both backup and storing videos, photos, etc. My question is this: What is the difference between SATA, PATA and IDE? Will the performance matter for my 3 year old iMac? Will the difference between 8MB and 16MB cache be a factor? Also I would like a case with both USB 2.0 and Firewire 400. What else do I need to look for in an external HD case? Is a fan a requirement? Will one case handle all SATA, PATA and IDE? Finally, what do I need to know about the chip set? Sorry...those are multiple questions, but I would be extremely grateful for any insight. Thanks everyone. Chris