Fast SCSI is an option that doubles the synchronous data-transfer speed. (Asynchronous transfers require a handshake for every byte transferred; synchronous transfers move a series of bytes before handshaking occurs, increasing the data-transfer rate.) The speed is achieved by removing excess margins from certain times and delays. To use the Fast SCSI option, you need high-quality cables. This option is compatible with normal synchronous SCSI; Fast SCSI:
Wide SCSI is an option that adds a second SCSI cable of 68 conductors. This cable provides a data path for 16-bit or 32-bit data. The path has separate handshaking signals and is for data transfer only. The transfer rate is either two or four times the current transfer rate of SCSI-1. With the second cable, SCSI-2 remains compatible with 8-bit SCSI.
(Check the Hardware Compatibility List for notes regarding SCSI adapters and any limitations with specific adapter cards.)