SCSI-bus Interface Overview

SCSI-bus Interface Overview

SCSI (Small Computer System Interface) is an industry standard I/O bus designed to provide host computers with device independence within a class of devices. All Silicon Graphics systems provide an interface to at least a single SCSI bus for peripherals that support the SCSI standard. Your device driver can place commands on the bus by using the SCSI host adapter driver. Systems with POWERchannel I/O processor boards support two SCSI interfaces per POWERchannel board; those with POWERchannel-2 boards support two native SCSI interfaces plus as many as six additional SCSI interfaces, if mezzanine boards are used, for a maximum of eight SCSI interfaces per POWERchannel-2 board. Systems equipped with VME-SCSI (Jaguar) boards provide two buses per board.

The drivers support all three SCSI standards, SCSI-1, CCS[11], and SCSI-2. Not all optional features are supported, and different systems support different features (such as synchronous, fast, and wide).

In addition, DMA address mapping registers allow noncontiguous physical memory to appear contiguous to the SCSI host adapter. This allows your driver to handle I/O across noncontiguous pages in a single transfer (scatter-gather). The IRIX operating system provides an interface that hides much of the complexity of the SCSI bus management.

[11] The Common Command Set (CCS) standard is superseded by SCSI-2.