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SCSI Tutorial
Small Computer System Interface, or SCSI, is a set of standards for connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and interfaces. SCSI is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners and CD drives. Every device attaches to the SCSI bus in a similar manner.
SCSI is a peripheral interface because up to 8 or 16 devices can be attached to a single bus. There can be any number of hosts and peripheral devices but there should be at least one host. SCSI is a buffered interface because it uses hand shake signals between devices. SCSI-1 and SCSI-2 have the option of parity error checking. With SCSI-3, all commands and data are error checked. SCSI is a peer to peer interface because the SCSI protocol defines communication from host to host, host to peripheral, and peripheral to peripheral.
SCSI is available in a variety of interfaces. The first was parallel SCSI, now called
SPI, which uses a parallel electrical bus design. As of 2008,
SPI was slowly replaced by Serial Attached SCSI (SAS), which uses a serial point-to-point design but retains other aspects of the technology. iSCSI uses
TCP/IP as a transport mechanism. iSCSI could thus address both the low-end and high-end markets with a single commodity-based product. Serial SCSI has a number of advantages over parallel SCSI: faster data rates, hot swapping, and improved fault isolation.
Here are a few of the most common SCSI interfaces:
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