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Ask the SCSI Expert.

Visit the SCSI Trade Association's web site ( to ask the SCSI Expert a question.

Q: I'm a software developer. I have an application which queries SCSI devices to gather configuration/asset information.

How do I query a SCS1 device to determine the device's bus speed? I can't find any mention of this in any of the SCSI-3 standards documents. Actually, I don't see any reference to "Ultra" or "Ultra2" or "Ultra160" in any of the SCSI3 standards on

A: Ultra SCSI, Ultra2 SCSI, and Ultra160 SCSI are the marketing names for the standards.

Following is the data that you need:

Ultra320 SCSI = SPI-4 Fast160 Paced data transfer = 6.25 ns

Ultra160 SCSI/Ultra3 SCS1 = SPI-3 Fast-80DT = 12.5 ns

Ultra2 SCSI = SPI-2 Fast-40 = 25 ns

Ultra SCSI = Fast-20 (Use SPI-2) = 50 ns

Wide Fast SCSI = Fast (Use SPI-2) = 100 ns Calculate transfer period)

Fast SCSI = SPI t Use SPI-2) = 100 ns (Calculate transfer period)

SCSI = SCSI-2 /Asynchronous- Narrow)

See the SPI-4 (Revision 7) table 5 for the Transfer period.

Q: We have a cable with the following printed on it: "E119932 AWM 2919 80C 30V VW-1 LOW VOLTAGE COMPUTER CABLE COPARTNER."

Does this mean that it only works for LVD devices? We have a SpectraLogic Gator/64000 (HVD) tape library that we want to connect to an IBM RS/6000 with a PCI Differential Ultra SCSI (Type 4-L) adapter (IBM Feature Code 6207). Would this cable cause as any problems connecting this system ?

A: The labeling on the cable is for UL certification purposes. Low voltage computer cable means that you cannot use the cable for applications over 30 volts at 80 degrees C, and it has nothing to do with SCSI. If this is a SCSI cable, then it should work fine for connecting HVD SCSI devices.

Q: How does a feed-through terminator work?

A: A feed-through terminator is used on the last bus connection. This type of terminator has both a male and a female connector, and is inserted between the last device and the cable.

It is normally used with scanners and low-end devices that do not need to have termination in the device.

I've seen demo cards for termination--for Multimode LVD/SE but no products. Normally on multimode, the termination is built into the cable assembly. This is typically done on the internal, "twist and fiat" cables. The last fiat will have both a 68-pin connector and a terminator that damps onto the cable with IDC (insulation Displacement connector) like the other connectors on the twist and flat cable.) in the "About SCSI" page. Select "Terms and Terminology" which has the speed, the interface and the corresponding cable lengths.

For the relatively newer LVD SCSI standards such as Ultra2. Ultra3, Ultra160 and Ultra320 SCSI it is easy---point-to-point 25 meters, multidrop 12 meters.
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Title Annotation:Tape/Disk/Optical Storage
Publication:Computer Technology Review
Date:Feb 1, 2002
Previous Article:Tape vs. disk: another view.
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