1. What is Ultra160 SCSI?

Ultra160 SCSI is the next generation of high performance SCSI technology that offers data transfer speeds of up to 160MB/sec. It is a term that is synonymous with Ultra3 SCSI and describes any device that combines Ultra2 SCSI with cyclic redundancy check (CRC), domain validation, and double transition clocking.

2. What are the differences between Ultra160 and Ultra3 SCSI?

Ultra160 SCSI is both a subset and an implementation of Ultra3 SCSI. As outlined by the ANSI SPI-3 specification, however, Ultra3 SCSI can incorporate one or more of five new features in any combination. As such, there could be as many as 63 variations that would qualify as Ultra3 SCSI-compliant. By incorporating a specific combination of optimized features, Ultra160 SCSI establishes an effective standard for performance and device compatibility.

3. How does Ultra160 SCSI achieve a transfer rate of 160 Mbytes/sec?

Double transition clocking enables Ultra160 SCSI to increase data transfer rates from 80 Mbytes/sec-the maximum rate for Ultra2 SCSI-to 160 Mbytes/sec without increasing the clock speed.

4. How does domain validation make Ultra160 more manageable?

With prior SCSI versions, the host controller sends a low-speed request (at approximately 5 Mbytes/sec) to each connected device asking for the rate at which it will transmit data. However, even though the device may be able to send and receive data at 80 Mbytes/sec, the connection may not support a rate that high and if there's a problem, the device is automatically rendered inaccessible. With domain validation, the transfer rate is actually checked at the negotiated rate-much like two modems negotiating transmission speeds prior to communication. If errors are detected, the rate is stepped down until the connection becomes error-free. In this way, if a connection can be made it will be made. Domain validation effectively manages the connection to reduce installation problems, eliminate costly support calls and lower the total cost of ownership.

5. Is Ultra160 SCSI more reliable?

Prior SCSI versions use parity checking to detect transmission errors. Because Ultra160 SCSI adds cyclic redundancy check (CRC), it's far superior for detecting errors during hot plug operations and high-speed data transfers. CRC is a proven international standard that checks all transferred data and adds significantly to data reliability.

6. Is Ultra160 compatible with prior versions of SCSI?

Yes. Ultra160 SCSI is compatible with all Ultra2 SCSI devices. When Ultra2 and Ultra160 devices are mixed, each device can at operate at its full-rated speed. Ultra160 SCSI is also compatible with LVD to single-ended transceiver technology, which provides support for all SCSI versions prior to Ultra2.

7. Is Ultra160 better than Ultra2 SCSI?

With 160 Mbytes/sec speed, Ultra160 SCSI is twice as fast as Ultra2 SCSI. And with the addition of management (domain validation) and advanced, CRC error correction capabilities, Ultra160 SCSI is clearly better than Ultra2 SCSI. Keep in mind, however, that Ultra160 is a superset of Ultra2 SCSI and, therefore, both use the same LVD (low voltage differential) interface. This means that Ultra160 SCSI controllers can support Ultra160 SCSI as well as Ultra2 SCSI drives, ensuring total compatibility with legacy devices.

8. Is Ultra160 SCSI better than Fibre Channel?

Ultra160 SCSI offers definite advantages over Fibre Channel. To begin with, Ultra160 SCSI is 60% faster than Fibre Channel which operates at a maximum speed of only 100 Mbytes/sec. Because SCSI has enjoyed much broader use, it also offers a wider array of devices from which to choose. This serves to keep costs down and make Ultra160 SCSI less expensive to implement. Compatibility is also at issue. While it is unquestionably one of SCSI's strengths, the history of Fibre Channel has demonstrated that compatibility between different products and versions can be a significant problem.

9. Is Ultra160 SCSI better than UDMA?

Nowhere does Ultra160 SCSI offer more advantages than when compared with UDMA. Most significantly, Ultra160 SCSI is 240% faster than UDMA which has a maximum data rate of just 66 Mbytes/sec. Another performance issue is UDMA's inability to support today's multi-tasking operating systems. Ultra160 SCSI, which fully supports multi-tasking, can significantly improve system performance especially in workstations and servers running Windows NT. UDMA also limits cable lengths to 18 inches-as compared with 12 meters for Ultra160 SCSI-effectively eliminating the ability to connect remote or external devices. Connectivity is another advantage. UDMA is only able to connect two devices while Ultra160 SCSI can connect up to 15 devices. Last but not least, UDMA does not support domain validation, so if there is a problem with the connection, UDMA drives will not operate properly.

10. When will Ultra160 SCSI be available?

Ultra160 SCSI is available now. Drives, controllers and cables are available through normal distribution channels and complete Ultra160 SCSI solutions are available through leading systems manufacturers.

11. Who makes Ultra160 products?

Ultra160 SCSI controllers and cables are available from Adaptec and Qlogic as well as other SCSI controller and cable manufacturers. Quantum, IBM, Western Digital and other major disk drive manufacturers are either currently producing Ultra160 drives or will be in production by late 1999. Compaq has announced systems using Ultra160 SCSI technology and will soon be followed by other leading systems suppliers.

12. Is Ultra160 SCSI more expensive?

In most cases Ultra160 SCSI costs no more to implement than Ultra2 SCSI technology. However, over the long term, Ultra160 may actually be less expensive. Because domain validation manages the connection and ensures drive availability, Ultra160 SCSI can dramatically reduce installation problems, eliminate costly support calls and lower the total cost of ownership.

13. What applications are best suited for Ultra160 SCSI?

High-traffic digital video environments and multi-node server clusters can easily benefit from the added speed and management of Ultra160 SCSI. Disk farms are another clear example where Ultra160 SCSI has the bandwidth to handle the additional load until a failed device can be replaced. Moreover, Internet service providers, corporate intranets, data mining and data warehousing operations can benefit from the ability of Ultra160 SCSI to negotiate transfer rates and guarantee connection during hot pluggable drive replacements.

14. What is Ultra160/m SCSI?

It is the same as Ultra160 SCSI. The "/m" has been removed to keep things simpler. Some Ultra160 product manufacturers may still use Ultra160/m. All of the features are the same.