Hardware components of the PC
Computer Buses
The SCSI bus
Small Computer Systems Interface (SCSI), pronounced scuzzy, is a standard for connecting peripheral devices such as hard disks, tapes, CDs, DVD-ROMs, scanners and printers to a computer via a standard hardware interface. Since being approved in 1986, the SCSI standard has continually undergone improvements and enhancements. There are currently three main SCSI standards in existence, SCSI-1, SCSI-2 and SCSI-3.
The SCSI specifications and their variations are listed below:
| SCSI Specification |
SCSI Name |
Transfer Rate |
Bus
Width (in Bits) |
Max
number of Devices supported per Channel |
| SCSI-1 | SCSI | 5MB/sec | 8 | 7 |
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| SCSI-2 | Fast SCSI | 10MB/sec | 8 | 7 |
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| SCSI-2 | Fast Wide SCSI | 20MB/sec | 16 | 7 |
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| SCSI-3 | Ultra SCSI | 20MB/sec | 8 | 15 |
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| SCSI-3 | Ultra Wide SCSI | 40MB/sec | 16 | 15 |
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| SCSI-3 | Ultra 2 SCSI | 40MB/sec | 8 | 15 |
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| SCSI-3 | Ultra 2 Wide SCSI | 80MB/sec | 16 | 15 |
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| SCSI-3 | Ultra 3 SCSI | 80MB/sec | 16 | 15 |
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| SCSI-3 | Ultra 3 Wide | 160MB/sec | 16 | 15 |
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| SCSI-3 | Utra 320 | 320MB/sec | 16 | 15 |
A key feature of the SCSI standard is the ability to connect multiple SCSI devices to a SCSI bus and controller card, referred to as a SCSI host adapter. The table above shows that between eight and sixteen devices can be connected to a single SCSI bus depending on the SCSI specification and since this number includes the host adapter, it effectively means between seven and fifteen SCSI devices can be used in parallel.
