On this particular score there isn't much of a competition: SCSI beats IDE/ATA hands
down. While SCSI is more involved and expensive to set up, once you make the appropriate
investments of money and time you get a bus that can be expanded relatively easily to
either 7 devices (with narrow SCSI) or 15 (with wide SCSI, which is what most new systems
use). On the other hand, IDE/ATA normally supports only four devices; you can expand this
to eight if you add an after-market IDE/ATA controller, but that can introduce its own
issues.
Of course, this advantage of SCSI only matters if you actually need this much expansion
capability. For most users, four device expandability is certainly sufficient, and eight
is definitely more than enough.
Next: Device Type Support
