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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 ]

Ultra320 SCSI

Description: Ultra320 SCSI is the current name given by the SCSI Trade Association to hardware being developed to the next generation of the SCSI parallel interface, as defined in drafts of the SCSI-3 Parallel Interface - 4 (SPI-4) standard. As the name implies, these drives support a maximum throughput of 320 MB/s using 80 MHz bus signaling and double transition clocking. This technology was at one point known by the name "Ultra4 SCSI", but it appears that this terminology will not be used going forward.

For more information, see the discussion of the SPI-4 standard and the information below. Bear in mind that SPI-4 and Ultra320 are still under development. Not much is known about the specific features that will be agreed to in this new version of the interface, so details are not yet complete.

Defining Standard: SCSI-3 / SPI-4 (in development).

Special Features: Fast-160(DT) data transfer; others not yet confirmed at this time.

Bus Width: Wide (16-bit) only.

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: 80 MHz bus speed; 320 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: SCSI Protocol Compatibility

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