In the world of technology, everything is getting faster. Processors have broken through the 500 MHz mark. Gigabit Ethernet can simultaneously send and receive data at 100 Mbytes/sec. Disk drives are capable of sustained transfer rates in excess of 20 Mbytes/sec. The PCI bus is expanding to 64 bits. And with the help of Moore's law, further increases will occur with clock-like regularity.

Given the reality of this scenario, system builders need an I/O technology with the ability to support the demand for higher speeds. SCSI has proven to be up to the task. Now, Ultra160 SCSI is ready to take SCSI to the next level. And not only will it keep pace with the need for speed, but Ultra160 SCSI promises to do so with seamless compatibility.

The Most Ultra3 SCSI Bang For The Buck
In the fall of 1998, the SCSI Trade Association (STA) created the term Ultra3 SCSI. It is used to describe any device that combines Ultra2 SCSI with one or more of six new features as defined by the ANSI SPI-3 specification. The problem with this specification, however, is that there could be as many as 63 variations that could qualify as Ultra3 SCSI. Even more worrisome, any two Ultra3 SCSI devices may not communicate at 160MB/sec because they don't include the same set of features.

To avoid such frustrations, Adaptec has adopted a feature set of Ultra3 SCSI -- called Ultra160 SCSI -- that offers the most advantageous and cost-effective implementation possible. So named to describe its 160 Mbyte/sec speed and added storage management capabilities, Ultra160 SCSI incorporates the three features of Ultra3 SCSI that specifically affect data transfer: cyclic redundancy check (CRC), domain validation and double transition clocking. Separately, each of these features provides significant advantages, but together they deliver a SCSI solution that is ideally matched to high-speed computer and networking technologies. As a result, the Ultra160 feature set is widely supported by industry-leading system manufacturers such as Hewlett-Packard and IBM, as well as a host of leading SCSI drive and component suppliers.

Building On Ultra2 SCSI
Ultra2 SCSI was the first version of SCSI to use low voltage differential (LVD) signaling. Ultra160 SCSI builds on that legacy to provide investment protection and ensure a smooth transition from Ultra2 SCSI. The cables, connectors and terminators are all the same. Plus Ultra160 SCSI host controllers can support Ultra2 SCSI devices. This allows mixing of Ultra160 and Ultra2 SCSI devices on the same bus. Ultra160 SCSI can be used with a LVD to single-ended converter to support legacy single-ended signaling used in SCSI devices prior to Ultra2 SCSI.

Building on Ultra2 SCSI, Ultra160 SCSI adds double transition clocking, domain name validation and cyclic redundancy check. Double transition clocking is the feature that enables Ultra160 SCSI to achieve 160 Mbyte/sec transfer rates -- an important ingredient for obvious reasons. However, domain validation and cyclic redundancy check provide benefits that may be even more significant.

Domain Validation Lowers Total Cost Of Ownership
With prior SCSI versions, the host controller determines what data transfer rate it will use with each connected device. This is accomplished through an INQUIRY command and subsequent data transfer -- a process conducted at up to 5 Mbytes/sec. Unfortunately, there's no guarantee that the connection can actually support the negotiated data rate which could be as high as 80 Mbytes/sec. And if there is a problem, the device is rendered inaccessible. With domain validation, once a transfer speed is negotiated, it is actually checked at the negotiated rate. If errors are detected, the rate is stepped down until the connection is error-free -- much like two modems negotiating transmission speeds prior to communication. The significance of this new feature is that if a connection can be made it will be made. In effect, domain validation manages the connection to ensure drive availability. This can dramatically reduce installation problems, eliminate costly support calls and lower the total cost of ownership (TCO).

CRC Adds Data Reliability
Ultra160 SCSI also adds cyclic redundancy check (CRC) -- a proven international standard incorporated into technologies such as Fast Ethernet, FDDI and Fibre Channel. While previous versions of SCSI have used parity checking to detect transmission errors, CRC adds an industrial-strength error detection capability that is far superior for high speed data transfer and during hot plug operations. CRC checks all transferred data (instead of a single byte) adding significantly to data reliability. What's more, CRC paves the way for increased data transfer rates in future versions of SCSI.

Where It Fits
Ultra160 SCSI is ideally suited for high traffic environments that can benefit from its added speed, management or both. Digital video environments, one of the most throughput intensive, will likely be the earliest to adopt Ultra160 SCSI. Multi-node server clusters are another example. When a server fails, it can bring I/O to a crawl. With twice the throughput of Ultra2 SCSI, Ultra160 SCSI host adapters have the bandwidth to handle the additional loads until a failed device is replaced.

In large disk farms the added speed of Ultra160 SCSI is an obvious plus. As databases expand into the terabyte range, information access requires more time. Ultra160 SCSI provides an easy-to-implement solution that can cut data transfer times in half. Moreover, its ability to negotiate transfer rates and guarantee connection during hot pluggable drive replacements can help maintain a higher level of drive availability -- even under less than ideal circumstances. Therefore, Ultra160 SCSI will be attractive to Internet service providers, corporate intranets, data mining and data warehousing operations.

Risk-Free Migration
As the next generation of proven I/O, Ultra160 SCSI promises to support advances in technology for the foreseeable future. Plus interoperability with Ultra2 SCSI and operability with a LVD to single-ended converter guarantees the preservation of legacy investments while eliminating the risks of migration. The future, therefore, is bright. Because with the added advantages of speed, reliability and built-in management, the transition to Ultra160 SCSI offers substantial benefits that are both painless and easy to implement.