What is the difference between SCSI-1, SCSI-2, Fast, Wide, Ultra Wide, and Ultra2?

The primary difference is in the command set used in the SCSI standard and the bandwidth, or maximum available speed of the devices.

SCSI-1 5MB/Sec 8 bit SCSI bus

SCSI-2 5MB/Sec 8 bit SCSI bus

SCSI-2 Fast 10MB/Sec 8 bit SCSI bus

SCSI-2 Fast Wide 20MB/Sec 16 bit SCSI bus

SCSI Ultra 20MB/Sec 8 bit SCSI bus

SCSI Ultra Wide 40MB/Sec 16 bit SCSI bus

Ultra2 Narrow 40MB/Sec 8 bit SCSI bus

Ultra2 Wide 80MB/sec 16 bit SCSI bus

Ultra3 Wide 160MB/sec 16 bit SCSI bus

Ultra-320 Wide 320MB/sec 16 bit SCSI bus

Ultra-640 Wide 640MB/sec 16 bit SCSI bus

Ultra2 speeds are available only when a Ultra2 host adapter is connected to Low Voltage Differential (LVD) devices on the LVD/SE port. If a single-ended (SE) wide or narrow SCSI-2 device is connected to the LVD-SE port, the performance for all devices reverts to SCSI Ultra.

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