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Brian Cryer's Glossary of IT Terms with Links

SCSI

SCSI

Small Computer Systems Interface. cf IDE. SCSI can be used to interface to any device that has a SCSI interface, this includes devices such as printers and scanners as well as the more traditional disk and tape drives.

SCSI adapters typically support one or two SCSI buses, each of which can support up to eight units. Each device on the SCSI bus is identified by a SCSI ID, which ranges from 0 to 7 (or sometimes 0 to 15). The SCSI adapter itself will occupy one of these SCSI IDs leaving 6 (or 14) available for other devices.

There are a number of different types of SCSI, reflecting its continuing development, and these are summarised in the following table:

SCSI Type		Data Width	Transfer Rate	Max devices	Max cable length (metres)
SCSI-1		8 bits	5MB/sec	7	6 m (SE) or 12 m (LVD)
SCSI-2	Fast (Narrow)	8 bits	10MB/sec	7	3 m (SE) or 12 m (LVD)
SCSI-2	Fast Wide	16 bits	20MB/sec	15	3 m (SE) or 12 m (LVD)
SCSI-3	Ultra (narrow)	8 bits	20MB/sec	7	1.5 m (SE) or 12 m (LVD)
SCSI-3	Ultra Wide	16 bits	40MB/sec	7 (SE) or 15 (LVD)	1.5m (SE) or 12m (LVD)
SCSI-4	Ultra 2 (narrow)	8 bits	40MB/sec	7	12m (LVD)
SCSI-4	Ultra 2 Wide	16 bits	80MB/sec	15	12m (LVD)
Ultra 3 (narrow)		8 bits	80MB/sec	15	12m (LVD)
Ultra 3 (wide)		16 bits	160MB/sec	15	12m (LVD)
Ultra 320 (wide)		16 bits	320MB/sec	16	12m (LVD)

Note:

The transfer rate is the maximum throughput of data on the bus, it does not indicate the maximum throughput of a device connected to the bus (for example the bus might be capable of 80MB/sec but a disk drive connected to it might be cable of only a fraction of that.)
The maximum cable length (which is the length from the adapter to the last device or terminator) may reduce as devices are added.

Relevant links:

www.ramelectronics.net/html/scsi_connecters.html - Pictures of various different types of SCSI connectors.
www.hardwarecentral.com/hardwarecentral/tutorials/36/1/ - Introduction to SCSI

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