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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+ SCSI

Description: Ultra160 SCSI--a.k.a. "Ultra160/m"--defines a specific subset of the features associated with Ultra3 SCSI. It was created to avoid the confusion associated with the various options that make up the Ultra3 SCSI definition. Ultra160+ SCSI is another feature set based on the five key enhancements to the SCSI interface introduced in the SCSI-3 Parallel Interface - 3 (SPI-3) standard. While Ultra160 SCSI defines three of the five key features as being mandatory, Ultra160+ SCSI refers to devices that implement all five of the key SPI-3 features.

To summarize the differences between these three related feature sets:

  • Ultra3 SCSI: At least one, and as many as five, of the main SPI-3 features.
  • Ultra160(/m) SCSI: Fast-80 signaling, CRC and domain validation are mandatory; QAS and packetization optional.
  • Ultra160+ SCSI: All five features are mandatory.

Aside from these definitional differences, all these terms refer to the same basic interface. See the discussion of the SPI-3 standard and the items below for more details.

Defining Standard: SCSI-3 / SPI-3.

Special Features: Ultra3 SCSI devices include support for all of the following five SPI-3 features:

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: Ultra320 SCSI

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