Ultra IDE vs. SCSI A system utilizing one or more SCSI devices saves some processor time due to the SCSI controller's on-board processor. However, EIDE changes the equation slightly. SCSI supports 7 devices per interrupt rather than 2. SCSI supports features like command queuing so you can send several commands to the disk at a time and let the disk decide how to service them fastest.
SCSI drives can be external.
Hard drives can be noisy, but some are much noisier than others. In our tests, Quantum drives, in general, seem to be among the quieter units out there. The fast Seagates were, in our tests, particularly noisy, producing a high-pitched whine. Of course, not every drive from a manufacturer will sound the same. For example, our Western Digital 4 gig drive is so quiet, we can barely hear it.