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The evolution of SCSI.

The evolution of SCSI


Ultra SCSI opens more lanes for your data traffic.

SCSI (Small Computer Standard Interface), pronounced “scuzzy,” enables you to connect your computer to a wide range of peripherals such as hard disks, CD-ROMs, printers, and scanners. SCSI is the way peripherals communicate with the main processor of your computer.

Three advantages of SCSI are its speed, compatibility, and expandability. In terms of speed, the fastest part of a computer is the processor, and throughout computer history the struggle has been to get information in and out of the processor as fast as possible. SCSI gets information in and out of the processor fast, and it keeps getting faster.


SCSI is highly compatible.

All Macintosh® computers come with a SCSI port, and you can order many PCs with a SCSI port. If your computer has a SCSI port, you can get another device with the same type of SCSI, plug it in, and the new device should work.

SCSI also makes it easy to expand. If you want to add another hard drive to your computer, you just connect via the SCSI port. And, if you want to add another CD-ROM tower or a printer, just daisychain up to seven additional devices—or in some cases, even more.

So if the history of computers has been shaped by getting information in and out of the processor faster, the history of SCSI has been shaped by trying to open a wider path in and out of the processor. The path in and out, or interface, can become a bottleneck that slows your data traffic.


As microprocessors get faster, hard drives get larger, and high speed becomes a necessity, slowdowns are becoming more frequent. The solution is Ultra SCSI.


How does Ultra SCSI work?

Until recently, Narrow and Wide SCSI set the standards for speed at 10 and 20 Megabytes per second (MBps) respectively. Ultra SCSI doubles those speeds—Narrow SCSI goes from 10 to 20 MBps and Wide SCSI goes from 20 to 40 MBps.

Surprisingly, the new SCSI speed limit isn’t reached by introducing radical new technology but by making subtle improvements in the delays and hold times of the chip, which adds up to great gains in speed. The improved times are the result of new semiconductor technology in the SCSI chip sets.

Because the technology isn’t radically altered, Ultra SCSI maintains backward compatibility with all previous SCSI standards. And because the internal drivers, firmware, and most of the drive circuitry remain the same as your existing SCSIs, you don’t have to change your current network topology. In fact, when you switch to Ultra SCSI, your peripherals won’t be affected at all—all you’ll see is better performance.


Some background on SCSI.

Ultra SCSI is the latest step in a long line of SCSI adaptations and improvements. Actually, the line is blurred between where SCSI-1 ended and SCSI-2 began,or where SCSI-2 ended and SCSI-3 began.

SCSI-1, the original standard approved in 1986, has evolved to meet the growing demands of the computer industry.

And although you could fill an encyclopedia documenting the improvements and revisions between the different levels of SCSI, the average SCSI user only cares about speed.

SCSI-1 supports transfer rates up to 5 MBps. SCSI-2, approved in 1994, usually supports 10 MBps but can go up to 20 MBps if combined with Fast and Wide SCSI.

SCSI-3 is found in many high-end systems and has transfer rates of 40 MBps.

At 20 and 40 MBps, Ultra SCSI leaves all previous standards behind. You don’t need to combine other forms of SCSI to get top speeds anymore.

Just imagine a two-lane bridge on a four-lane highway: If there’s very little traffic, things flow smoothly. But when traffic increases, you start to get a backup at the bridge. However, if you install a wider bridge with the same number of lanes as the highway, there shouldn’t be a bottleneck at all. In short, the SCSI bus, Ultra SCSI opens more lanes for traffic.


Serial SCSI.

Microsoft® Windows® 98 supports the Universal Serial Bus (USB), which enables SCSI to run on USB or fibre Channel—an exciting possibility.


What's new? SCSI-5.

SCSI-5, a new type of connector interface, is also called VHDCI (Very High-Density Connector Interface) or an 0.8-mm connector. It's similar to the SCSI-3 MD68 connector in that it has 68 pins and a much smaller footprint.

SCSI-5 is designed for next-generation SCSI connections where high performance is a key requirement. It's expected to become the connector of choice for advanced SCSI multipoint applications, such as UltraSCSI Fast-40, and the new Low-Voltage Differential Signal (LVDS) technology.

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