Ultra320 SCSI Frequently Asked Questions
1. What is Ultra320 SCSI?
Ultra320 SCSI is the seventh generation of SCSI I/O technology. Its dominant feature is its increased speed of 320 MBytes per second. Other features include; paced data transfer, a free running clock, a training pattern at the beginning of a transfer series, skew compensation, driver pre-compensation and/or optional receiver Adjustable Active Filter (AAF). Ultra320 SCSI devices all support packetized protocol and may support Quick Arbitration and Selection (QAS). Expander communications techniques have also been defined.
2. What are the differences between Ultra320 SCSI and Ultra160 SCSI?
Differences include paced data transfer (see answer # 1.), doubling of the speed, and expander communications.
3. How does Ultra320 SCSI achieve a transfer rate of 320 MBytes/sec?
A free running clock and driver pre-comp and/or optional receiver AAF, are the main keys to the higher speed. The clock runs twice as fast in Ultra320 SCSI as in Ultra160 SCSI.
4. What is Packetized SCSI and how does it benefit Ultra320 SCSI?
Packetized SCSI transfers bundled commands, messages and status bytes at full data transfer speeds, reducing the protocol overhead. Packetization also allows the transfer of multiple commands or data from multiple I/O processes in a single connection.
5. What does QAS do?
Quick Arbitration and Selection reduces the bus arbitration and device selection time by eliminating bus free time. Bus free time is the interval at which a device can hand the bus to another device without entering a new arbitration phase.
6. Is Ultra320 SCSI just as reliable as Ultra160 SCSI?
Pre-comp and/or optional receiver AAF, skew compensation and SCSI Domain Validation (SDV) ensure that Ultra320 SCSI systems are capable of running reliably at higher speeds.
7. Is Ultra320 SCSI compatible with prior versions of SCSI?
SCSI devices are always backward compatible. When newer SCSI devices are attached to a system with devices from a previous generation, the newer devices will back down to the maximum operating speed of the older generation when they are talking. When not talking to older devices, the newer devices operate at their normal speeds.
8. Is Ultra320 SCSI better than Ultra160 SCSI?
Yes. Ultra320 SCSI adds greater speed, reduced overhead, training patterns, compensation for system losses and system mapping with diagnostic capabilities for expanders. Ultra320 SCSI is better protected since the command, message, and status information are protected by CRC.
9. Who makes Ultra320 SCSI products?
Ultra320 SCSI has wide support in the industry. All the SCSI adapter and hard disk vendors have products that have been, or will be introduced in 2001.
10. What applications are best suited for Ultra320 SCSI?
Ultra320 SCSI is best suited for servers, network storage, high-end workstations and RAID storage applications.
