SCSI

 

Abbreviation of small computer system interface. Pronounced scuzzy, SCSI is a parallel interface standard used by Apple Macintosh computers, some PCs, and many UNIX systems for attaching peripheral devices to computers. All Apple Macintosh computers starting with the Macintosh Plus come with a SCSI port for attaching devices such as disk drives and printers.

 

SCSI interfaces provide for faster data transmission rates (up to 40 megabytes per second) than standard serial and 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 new 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: Uses an 8-bit bus, and supports data rates of 4MBps

Fast SCSI: Uses an 8-bit bus, and supports data rates of 10MBps.

Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20MBps.

Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20MBps.

Ultra Wide SCSI: Uses a 16-bit bus and supports data rates of 40MBps.