What is QAS?
• Answer: Quick Arbitration and Selection, an optional method of arbitration defined in the SPI-3 document of SCSI-3 for Ultra 160, is designed to eliminate overhead and speed up data transfers on the SCSI bus by skipping over the bus free phase. A device with QAS will arbitrate for the bus immediately after the last device on the bus sends a disconnect instead of waiting for the bus free phase that normally occurs after a disconnect. Included in QAS is the need for SCSI “fairness” (Refer to SPI-3, Annex B) which prevents fast devices with a higher priority from “hogging” the bus and preventing devices with a lower priority from gaining control of the bus. QAS is negotiated in the arbitration phase.
Related Questions
- I have received an Experian QAS purchase order referencing the standard supplier terms and conditions - where are these and which ones are relevant to me?
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