From what i've been able to find on the web, the jumper is installed to force the drive to work with 1st generation SATA controllers on older computers. I haven't been able to find a definitive answer on the Apple FAQ's about what version of SATA controller they use, but you have to assume that it would be the latest and fastest. I got two Seagate drives in the last couple of weeks and they both had the jumper installed to force the slower data transfer speed. I pulled both of them. I haven't pulled the original WD 320 gig drive shipped with my 1/08 Mac Pro to see if it has a jumper installed. Anybody else checked theirs?