SCSI-1 SCSI-2 Fast SCSI-2 Wide SCSI-2 Fast Wide SCSI-2
Intro. 1986 1994
Data Bus 8-bit 8-bit (supports double speed) 8-bit 16-bit 16-bit
Speed 5 mpbs 5 mbps 10 Mbps 10 Mbps 20 Mbps
Cable Length
6 meters 6 meters 3 meters SE
25 meters HVD
3 meters SE
25 meters HVD
3 meters SE
25 meters HVD
# of Devices
8 16 16
SE - This is "Single Ended" technology which is used to transmit one bit over it's own wire (therefore, for 8 SCSI systems, there will be 8 wires within the ribbon cable dedicated to just the data path).

HVD - This is High-Voltage Differential technology. This system sends a data signal over a pair of wires so that it can resist interference much better, hence the ability to support longer cables lengths.

The cabe lenghts shown above indicate the total allowable length of cable used in that system (not the length between devices).

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