PC Hardware in a Nutshell, Second Edition

SCSI

We’ll devote less space to SCSI than IDE, since IDE drives dominate the PC platform, but we will try to hit the high points of SCSI. SCSI (Small Computer Systems Interface) is a general-purpose I/O bus that is used in PCs primarily for connecting hard disks and other storage devices, and secondarily for connecting a variety of devices, including scanners, printers, and other external peripherals. Although common in the Apple Macintosh world, SCSI has remained a niche product in PCs, limited primarily to network servers, high-performance workstations, and other applications where the higher performance and flexibility of SCSI are enough to offset the lower cost of ATA.

SCSI Standards

SCSI is confusing because of the proliferation of terms, many of which refer to similar things in different ways or to different things in similar ways. There are actually three SCSI standards, each of which refers not to any particular implementation, but to the document that defines that level.

SCSI-1

The Small Computer Systems Interface (SCSI) standard was adopted in 1986 and is now obsolete. Originally called simply SCSI, but now officially SCSI-1, this standard defines a high-level method of communicating between devices, an Initiator (normally a computer) and a Target (normally a disk drive or other peripheral). SCSI-1 permits data to be transferred in asynchronous mode (unclocked mode) or synchronous mode (clocked mode), although commands and messages are always transferred in asynchronous ...