Snip that I did as a result, I had a major learning experience. I learned that the technology of my mirrored door G4 represented a significant technical plug-and-play milestone by Apple toward rendering insignificant the master/slave jumper settings. I also learned that the new serial ATA drives were manufactured to accommodate the new plug and play technology. There seems to be a consensus of information that connections for drives mounted in the front tray make the G4 operate a little slower than the rear tray connections. Mine now seems a little slower. My new question is this: If I move the 750 GB Seagate, with the OS on it, from the front to the rear tray, and move one of the rear IBM drives in the rear tray to the front, will my computer still recognize the Seagate as my startup disk, and boot up, or will there just be a smoky hole in the ground where my computer was? Snip Forget the master slave business. You should be able to use Cable Select on that MDD. Set both drives to Cable Select. Much simpler. Kathi