Small Computer Systems Interface (SCSI)

SMALL COMPUTER SYSTEMS INTERFACE (SCSI) describes a 50-pin interface standardized by the American National Standards Institute. The advantage of the SCSI interface is that it can handle much higher data transfers between computer and device. The SCSI drives (hard drives which have the SCSI interface) are usually chosen for high-end applications such as network servers.

A SCSI hard drive requires a separate SCSI controller adapter card. There have been several upgrades of the original SCSI standard. They have been identified as SCSI-I, SCSI-II, SCSI-III, etc. The devices produced under one standard (upgrade) are not compatible with devices produced under an improved standard (upgrade).

SCSI is an interface standard, therefore other types of devices, such as CD-ROMs, can also be added to the same controller adapter card. A single SCSI controller can control up to 7 SCSI devices. Each SCSI device has an input connector and output connector so that the devices can be daisy-chained together. The last device must have a terminating resistor pack plugged into the output connector of that device. Every SCSI device has a jumper block or switch which can be set from 1 to 7 so that the controller can identify one device from another on the daisy chain.

SCSI drive characteristics are not set in BIOS. If the SCSI hard drive is the only hard drive in a computer, the BIOS is set to 'No drive installed'. A SCSI device requires its own software for installation, low-level formatting and operation. Disk partitioning and high-level formatting are done with FDISK. Because the SCSI controller is not tied to the BIOS, the SCSI drive can coexist with another drive type in the same machine (check with the manufacturer).