Black Box Explains...SCSI interface.
Small Computer System Interface (SCSI), pronounced “scuzzy,” is a standard used to connect computers to such peripherals as CD-ROM drives, hard drives, scanners, and laser printers.
The SCSI interface has the advantage of being significantly faster than other interfaces such as IDE. CD-ROM towers with a SCSI interface give you faster transfer speed because transfer speed is determined by the type of interface rather than by the speed of the CD-ROM drive. SCSI drives consistently outperform IDE drives regardless of drive speed.
SCSI devices are linked together to form a SCSI chain. It is recommended that slower SCSI types such as SCSI-1 or narrow SCSI should be connected last on the SCSI bus&—if they were connected first on the bus, they would slow down the faster SCSI interfaces.
A SCSI chain can contain up to seven devices plus the computer. Each device, including the computer, has its own unique SCSI ID number from 0 through 7, with the computer usually being number 7. All SCSI devices in a chain must have a different number—if more than one device has the same number, your system will crash.
It’s important to be sure of the SCSI ID number of all SCSI devices whenever you add a new device. Usually, you can change the SCSI ID with a small dial or DIP switches on the back of the device.