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SCSI. SCSI Basics. Standard for communication between subsystem of peripheral devices and system bus Bus can contain/be used by up to 7 or 15 devices Bus requires controller embedded on motherboard or host adapter inserted into an expansion slot
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SCSI Basics • Standard for communication between subsystem of peripheral devices and system bus • Bus can contain/be used by up to 7 or 15 devices • Bus requires controller embedded on motherboard or host adapter inserted into an expansion slot • Faster, more expensive, more difficult to install than similar IDE devices
The SCSI Subsystem • Enables two devices on SCSI bus to pass data between them without going through CPU • Requires SCSI controller and unique SCSI IDs assigned to each device, including host adapter
Host Adapters • Manage all devices on SCSI bus • Support internal and external SCSI devices • Form a single daisy chain with devices
Variations in SCSI • Bus width • Signaling methods used on SCSI cables • Connectors used with SCSI cables • Termination • SCSI-1, SCSI-2, and SCSI-3
Bus Width • Narrow SCSI • 8-bit data path • Uses a cable with a 50-pin connector (A cable) • Wide SCSI • 16-bit data path • Uses a cable with a 68-pin connector (P cable)
Connectors Used with SCSI Cables • Not affected by signaling method used • Types vary in shape and pin density; can be connected with adapters • Two main types: • 50-pin (A cable) • 68-pin (P cable)
Termination • Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain • Required at each end of a SCSI chain
Major Versions of SCSI • SCSI-1 (Regular SCSI) • 50 pin cable • 8-bit data bus • 7 possible devices • 5MHz sync and async operations • SCSI-2 (Fast SCSI) • 50 pin cable High density. Fast SCSI(10MHz) • 16-bit data bus • 15 possible devices • Mandatory parity checking
Major Versions of SCSI (continued) • SCSI-3 (Ultra SCSI) • Supports both parallel and serial data transmission • Supports FireWire connections • Data transfer of 320 MB/sec • Includes SPI standard