This is where SCSI names start getting a little muddy. Ultra is a term that applies to the emerging SCSI-3 standard, which may double the speed yet again. Fast Ultra and Fast UltraWide do not exist-at least not yet. These speeds show why SCSI is popular for internal hard drives and other storage devices. SCSI, unlike EIDE, lets you daisychain several devices together.
Most SCSI devices have an auto-termination feature to tell the adapter where the chain ends.
Because the SCSI adapter card usually uses address 7, and address 0 or 6 is for bootable SCSI hard drives, avoid those three addresses when installing your new SCSI peripheral. You can attach devices safely at addresses 1 through 5, linking from one to another without adding another SCSI adapter card. By the way, all these different SCSI flavors are backward-compatible. USB looks like a strong contender to succeed SCSI in some areas. USB won't gain much popularity for storage devices except perhaps tape backups.