SCSI CARDS

SCSI (Small Computer System Interface) is a standardized interface that provides a method for adding devices to your computer. The card that plugs into the expansion slot is called a host adaptor. A single SCSI host adapter will support up to 8 or 16 physical units (called SCSI ID's), one of which must be the host adapter. The other 7 or 15 may be other devices, and you may have as many as 4 host adaptors in your computer, so it's possible to add up to 60 devices to one computer. There are even dual channel adapters, so you could double that figure!

Most of the things you might want to add to your computer come in SCSI packages - hard drives, CD/CDR/CDRW drives, LS-120 SuperDisk or Zip Drives, tape drives, scanners, etc. SCSI CDR drives have been especially popular on older systems because data transfer between two SCSI devices is very fast and, if your CD-ROM drive and your CDR drive are both SCSI, you get a much cleaner and faster transfer of data between the two drives causing many fewer ruined CDs.

The installation of a SCSI Host Adapter card is the same as any other expansion card. First you'll need an open expansion slot, then you'll need to make sure you have an IRQ available (one in the range that your SCSI card can use) and that there will be no conflict with the I/O location your SCSI card will use. You will also need to check on the DMA your Host Adapter will use and make sure there is no conflict there, as well. All these things are usually adjustable, either through software or jumpers, on your Host Adapter.

Once you've physically installed the SCSI card, you must install the drivers for the SCSI card you've installed. Drivers are special software programs that convert information from a device (in this case the SCSI Interface) to information the operating system of the computer can use, and vice-versa. So the driver installed *MUST* be written for the specific SCSI Host Adapter you installed and for the specific operating system your computer is using. Fortunately, Windows9x has most of the more popular SCSI Host Adapter drivers built-in (especially for the largest manufacturer, Adaptec) so that is usually not a problem.

There are several flavors of SCSI which came about as SCSI matured and they usually refer to the age and/or speed and bandwidth of the system. SCSI-1, or the original SCSI standard, for instance, was mainly for 8 bit systems and used a fairly slow clock speed and a 50 pin, edge connector type external cable. SCSI-2 came along fairly quickly with higher speeds and a 50 pin high-density external connector and the SCSI-3 standard has much higher speeds and the external cable is a 68 pin high-density connector.

You should understand that the information above is not totally true or accurate, and certainly not complete, but is offered simply as reference - it's mostly true and gives you a taste of SCSI flavors. Book have been written about SCSI and you can get lost in all the information available. The largest manufacturer of SCSI cards, Adaptec, has a lot of information about SCSI on their web site and would be a good place to start if you wanted to learn more.

Additional Information:
Basic SCSI
Why SCSI

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