Wide SCSI


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Wide SCSI

(hardware, standard)
A variant on the SCSI-2 interface. It uses a 16-bit bus - double the width of the original SCSI-1 - and therefore cannot be connected to a SCSI-1 bus. It supports transfer rates up to 20 MB/s, like Fast SCSI.

There is also a SCSI-2 definition of Wide-SCSI with a 32 bit data bus. This allows up to 40 megabytes per second but is very rarely used because it requires a large number of wires (118 wires on two connectors). Thus Wide SCSI usually means 16 bit-wide SCSI.

Wide SCSI

A SCSI interface that transfers 16 bits in parallel rather than 8 bits. See SCSI signaling.
References in periodicals archive ?
SCSI-2 Same as SCSI, but with a50-pin connector instead of a 25-pin connector to support multiple devices Wide SCSI Uses a wider cable (168 cable lines to 68 pins) supporting 16-bit transfers Fast SCSI 8-bit bus, but doubles the clock rate supporting data rates of 10 MBps Fast Wide 16-bit bus supporting data rates of 20 MBps SCSI Ultra SCSI 8-bit bus supporting data rate of 20 MBps SCSI 3 16-bit bus supporting data rates of 40 MBps.
Table 1: Maximum SCSI cable lengths STA TERM Max Bus Bus MAXIMUM BUS LENGTH Max Speed, Width, Number of Mbytes/Sec Bits SE HVD LVD SCSI IDs Slow SCSI (SCSI-1) 5 8 6m 25m -- 8 Fast SCSI (SCSI-2) 10 8 3m 25m -- 8 Fast Wide SCSI 20 16 3m 25m -- 16 Ultra SCSI (SCSI-3) 20 8 1.5m 25m -- 8 Ultra SCSI 20 8 3m 25m -- 4 Wide Ultra SCSI 40 16 1.5m 25m -- 16 Wide Ultra SCSI 40 16 3m 25m -- 4 Ultra2 SCSI 40 8 -- -- 12 * 8 Wide Ultra2 SCSI 80 16 -- -- 12 * 16 Ultra160 SCSI 160 16 -- -- 12 * 16 Ultra320 SCSI 320 16 -- -- 12 * 16
On a Wide SCSI bus, you can use IDs 15 through 00, but 07 is still the highest priority.
If you are attaching a narrow device to a wide SCSI bus, you must use the "lower byte." The reason is that the narrow device uses the lower byte only.
Q: Will an Ultra2 SCSI drive, work on a Wide SCSI (68 pin) or SCSI II (50 pin)?
SCSI went from a bus that had 1.5MB data transfers to one that maintained 40MB transfers on wide SCSI, and was under pressure to go faster.
SPI made the wide SCSI bus practical by adding a single 68-pin P cable.
Some of the new features incorporated into SCSI-2 include wide SCSI with data transfer at bus widths of 16 and 32-bits.