Q When talking about computers, what does SCSI mean?
A SCSI is an abbreviation for Small Computer System Interface. Pronounced “scuzzy,” it is a parallel interface standard used by Macs, PCs and many Unix systems for attaching peripheral devices to computers.
SCSI interfaces provide faster data transmission rates (up to 40 Mbytes per second) than standard serial or parallel ports. In addition, you can attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.
Although SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be incompatible. For example, SCSI supports several types of connectors.
While SCSI is the only standard interface for Macintoshes, PCs support a variety of interfaces in addition to SCSI. These include IDE, Enhanced IDE and ESDI for mass storage devices, and Centronics for printers. You can, however, attach SCSI devices to a PC by inserting a SCSI board in one of the expansion slots. Many high-end PCs come with SCSI built in. Note, however, that the lack of a single SCSI standard means that some devices may not work with some SCSI boards.
The following varieties of SCSI are currently implemented:
SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MBps.
SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector for 16-bit transfers, and supports multiple devices. This is what most people mean when they refer to plain SCSI.
Wide SCSI: Uses a second cable (called a B-cable) to support 32-bit transfers.
Fast SCSI: Uses a 16-bit bus, but doubles the clock rate to support data rates of 10 MBps.
Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.
Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.
SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide SCSI. Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.
Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.
From QST October 2000
