I had IDE, then switched over to SCSI and of all the upgrades I've made to my computer, this one shocked me the most (with the possible exception of getting my first 3d accelerator). I was completely stunned at how many things were suddenly much faster, particularly things like file searches and scandisk. Nowadays IDE drives are much faster then they were when I switched (originally went from an 8.4 gig 5400 RPM, to a 9.1 gig 10,000 RPM), but all of the computers I use which have IDE today are still noticeably slower then my dated SCSI drives (and much more so slower then my new SCSI drives). The other great thing about SCSI is the ability to add many more drives. I currently have 2 SCSI controllers (one single channel Ultra160 and one dual channel Ultra160 RAID) I have 5 hard drives, 5 CD drives (1 CD-ROM, 1 DVD-ROM, and 3 CD burners) and a Tape drive. I could easily run all of this off of my single channel controller, the only reason I don't is I got the RAID card for christmas, and it's a lot faster. With my 11 drives, I can still add 34 more drives to my system before I'd need another controller. 3 of my hard drives are also hot swappble, because they're SCA and plugged into an SCA backplane. I've actually pulled my boot drive out of the system while it was running, and nothing crashed, when I put the drive back, in spun up again, and was accessable as normal. The last main advantage to SCSI in my opinion is the CPU Utilization, SCSI runs at extremely low CPU utilization, which leaves resources free for your system, and can cause less problems (particularly when burning a CD). I can burn 3 CDs at once (no burn proof on any of my drives) while still working on other things as I normally would. There is only one disadvantage to SCSI, and that is cost. It's definately not worth it for everyone, but it was well worth it to me, and I'm sure there are other people out there who feel the same way.