Adaptec PCM-3420, PC/104 manual

SCSI, this can result of SCSI bus data transfer rates of 20 MBytes/ sec (with a 16-bit bus) or 40 MBytes/sec (with a 32-bit bus).

SCSI may now transfer data at bus widths of 16 and 32 bits. Commands, status, messages and arbitration are still 8 bits, and the B-Cable has 68 pins for data bits. Cabling was a confusing issue in the closing days of SCSI-2, because the first project of SCSI-3 was the definition of a 16-bit wide P-Cable which support- ed 16-bit arbitration as well as 16-bit data transfers. Although SCSI-2 does not contain a definition of the P-Cable, it is quite possible that within the year, the P-Cable will be most popular non-SCSI-2 feature on SCSI-2 products. The market responds to what it wants, not the arbitrary cutoffs of standards committees.

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5 4 PCM-3420 User's Manual