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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Interfaces and Configuration | Small Computer Systems Interface (SCSI) | SCSI Data Transfer Modes and Feature Sets ]

Ultra160 (Ultra160/m) SCSI

Description: The SCSI Trade Association created the Ultra3 SCSI marketing program to identify drives implementing some or all of the main features associated with the SCSI-3 Parallel Interface - 3 (SPI-3) standard. This created a controversy, because hardware could be called "Ultra3 SCSI" even if it implemented only one of the five key features in the SPI-3 standard. Hardware makers feared this would create compatibility problems, especially since some "Ultra3 SCSI" devices might not support the 160 MB/s transfer speed that is the key feature of the new standard.

To address this possible source of confusion, several SCSI hardware companies decided to stay way from the "Ultra3 SCSI" label, and created a specific feature set called Ultra160/m, where the "160" refers to the maximum throughput of the interface--the "/m" means "maximum" or "manageability". The "/m" suffix was later dropped to "prevent confusion", yielding just Ultra160. Once again, this created more confusion, not less, because many people think Ultra160 and Ultra160/m are different. (Hardware makers! Stop confusing people by renaming standards to avoid confusing people! ;^) )

Note: Ultra160+ is a different subset of Ultra3 SCSI, and is not the same as Ultra160 or Ultra160/m. Aren't standards great? ;^)

See the discussion of the SPI-3 standard and the items below for more details on Ultra160 SCSI. Incidentally, in 1999 the SCSI trade association recognized the Ultra160 feature set; it also seems to be sticking with that terminology going forward, given that the next generation of SCSI will be called Ultra320 and not "Ultra4".

Defining Standard: SCSI-3 / SPI-3.

Special Features: Ultra3 SCSI devices include support for the following three SPI-3 features:

The following features are considered optional for Ultra160:

Bus Width: Wide (16-bit). Narrow mode is not supported.

Signaling Method: LVD only. (Multimode drives may optionally run in SE mode, but throughput will drop to Fast-20 (Ultra) levels.)

Signaling Speed and Bus Throughput: 40 MHz bus speed; 160 MB/s.

Number of Devices Supported: 16 for cables up to 12m in length; 2 for cables over 12m.

Termination: LVD termination.

Cabling and Maximum Cable Length: "P" cable (68 pins). Maximum of 25m if no more than 2 devices are used, otherwise 12m.

Next: Ultra160+ SCSI

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