STA clears up SCSI naming confusion

Posted on January 01, 2000

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by Dave Simpson

After months of political infighting, the SCSI Trade Association (STA) recently firmed up the nomenclature for current and next-generation SCSI devices.

According to Harry Mason, STA chairman and strategic alliance director at LSI Logic, Ultra160 SCSI devices operate at 160MBps and must include double-edge clocking, cyclical redundancy checking (CRC), and domain validation (see definitions below).

Ultra3 SCSI devices will in almost all cases include these Ultra160 baseline features, but may or may not include packetization and quick arbitrate and select (QAS). "Ultra160 defines the minimum level of interoperability for the Ultra3 SCSI standard," explains Mason.

If you're evaluating Ultra160 or Ultra3 SCSI products, here are the terms you'll need to know:

  • Cyclical redundancy checking (CRC) protects data loss in the event of a poor connection or while hot-swapping a new drive into a system.
  • Domain validation helps ensure fastest data transfer rates possible. If the highest rate is not possible, domain validation allows the device to shift to a lower data transfer speed before the transfer begins.
  • Double-edge clocking allows SCSI to continue doubling performance. Current SCSI devices can operate at up to 160MBps; next-generation products will run at 320MBps and 640MBps.
  • Packetization allows multiple commands, messages, status, and data to be transferred between SCSI devices in two data phases and at the fastest negotiated data rate.
  • Quick arbitrate and select (QAS) provides faster arbitration to reduce connect/disconnect time on the SCSI bus. Implemented by one QAS-supported device relinquishing the bus to a second QAS-supported device waiting for bus time without entering a new arbitration phase.

    STA also settled on naming conventions for next-generation SCSI standards: Ultra320 and Ultra640, previously code-named Ultra4 and Ultra5 SCSI. Ultra320 will support data rates up to 320MBps and, according to Mason, will include all five features described above as well as additional levels of domain validation. For more information, visit www.scsita.org.

    Click here to enlarge image

    Harry Mason
    STA chairman and LSI's strategic alliance director


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