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A SCSI controller is a card that, when installed in your computer, allows you to
easily connect up many hardware devices that are compatible with the SCSI hardware interface by daisychaining them together.
Compared to other similar hardware interfaces, such as IDE, SCSI allows data to be transferred between the computer and SCSI devices very quickly, making it preferred in high-end computers in which performance is critical.
You should consider installing a SCSI controller if you are planning to add at least one hardware device to your computer that you want to function as quickly as possible.
You may also want to consider a SCSI controller if you are planning to add one device and you want to be able to easily add more devices if need should arise.
Examples of SCSI devices include hard disk drives, CD-ROM drives, external removable media drives, and scanners.
SCSI technology has been around for nearly 20 years and there are now several different forms of it, including SCSI, SCSI-2, and SCSI-3.
Each new form is faster and more efficient than the last, yet remains compatible with older SCSI devices.
In addition, there are different varieties within each form, such as Fast SCSI-2 and Wide SCSI-2.
Each different variety is designed to meet the demands of a certain type of device.
Most SCSI controller cards have both an external and an internal port for connecting devices, which should be more than enough expansion capacity for most people.
All SCSI controllers of a certain variety will probably provide almost equal performance, regardless of the brand name or particular make.
Therefore, if you are considering a SCSI controller, you only must make sure that it is compatible with and appropriate for the devices that you want to use it with.
For example, if you plan to use the controller with a hard drive or CD-ROM drive and want the best performance possible, install a controller with an internal connector that supports high data-transfer speeds.
A good choice might be an Ultra2 SCSI card, which incorporates the latest technology to outperform the data transfer rates of the standard IDE and EIDE interfaces.
On the other hand, if you plan to use the controller only with less demanding devices such as a scanner or a Zip drive, you can save money and buy a cheaper controller.
A SCSI-2 card with only an external connection port (the installation of which is described here) would probably be perfectly adequate.
SCSI controllers range in cost from about $70 to over $500.
Before buying a SCSI controller, make sure that the number of pins that it has on its connectors is compatible with the devices that you want to use.
Also ensure that there is a free, empty expansion slot inside your computer for the type of card (PCI or ISA) that you want to install.
Finally, if you plan to use your controller with external devices, make sure that you have proper SCSI cables.
They should accommodate the appropriate numbers of pins for the controller and the devices you plan to install, and be long enough to connect the devices together and to the back of the computer.
SCSI cables come with SCSI devices and with controllers, usually in lengths of 3 feet or 1 foot.
If you need a longer length of cable (6' is the largest commonly-found size), you will probably have to purchase it separately.
A Phillip's screwdriver and about 40 minutes of time are required to install a SCSI controller.
Click here for a list of SCSI controller manufacturers.
the installation
- Make sure the computer is turned off.
- Carefully disconnect all of the cables from the back of your computer, place the computer on a stable working platform, and remove the outer case.
Discharge any static electricity from your body by touching the computer's power supply.
- Locate a free expansion slot that matches your new SCSI controller's interface (PCI or ISA).
If the slot you have selected was previously unused, you will need to remove a metal strip (blocking the opening next to the expansion slot) by removing the screw holding it in place.
Put the screw in a place where it will not get lost.
- Remove your SCSI controller card from its protective bag.
Line up the edge of the card containing the metal contacts with the slot and push the card in firmly with its metal plate facing the back of the computer.
If you find it too difficult to push the card in directly, insert one corner of the card into the expansion slot, then push the rest of the card into place.
Secure the card with the previously removed screw.
- Replace the computer's outer case, and carefully move the computer back to its original position.
Reconnect all of the original cables.
- Connect your external SCSI devices to the controller and to each other using SCSI cables. Firmly
press the end of a cable onto the appropriate port of a device or onto the port on the
controller, and tighten the thumb-screws. Use the following guidelines:
- At minimum, one device must be connected to the controller. Additional devices are "daisychained"
to the first device. For example, a cable is run from the "SCSI-out" port of the
first device to the "SCSI-in" port of the second device, and so on.
- If you have only one device, connect the adapter to the device directly
- If you have multiple devices, a terminator must be attached between the cable and
the "SCSI-in" port of the final device on the chain.
This is a small piece of hardware about the size of one SCSI connector to which a SCSI cable and a SCSI device can simultaneously be attached.
Terminators usually come with a SCSI device with the controller.
- In order for any device to function, all of the devices between it and the card
must be turned on. Therefore, place devices that are likely to be used more often
(or that will require more bandwidth, such as disk drives) closer on the chain to
the controller.
- The chain can be at most 15 feet long. There can be at most 7 devices on the chain,
not counting the controller.
- Each device must have a different SCSI ID.
Consult the manuals of each of your devices to find out how you can change its ID.
Valid IDs are from 0 through 6; higher IDs may be shown as possible
settings on some devices, but are allocated for self-testing procedures.
- Turn on the SCSI devices you want to use, and then start up the computer. A message may
appear on the screen as the computer starts up indicating that the card has been installed
properly. Windows should recognize the new controller and attempt to install the drivers for it.
It may prompt you to insert the Windows 9x CD or the CD or floppy disk that came with the controller.
You may also have to supply Windows with the drivers for your devices in a similar way.
- Click on the Start button, move the cursor to Settings, and click on Control Panel.
Double click on the System icon.
Click on the Device Manager tab, and expand the SCSI Controllers category.
There should be an entry for your newly installed SCSI controller.
If there is no entry, or if the entry has a yellow circle with an exclamation mark next to it, your controller is not configured properly or there is a hardware conflict of some sort.
Consult the manual that came with your controller and/or use the Windows Troubleshooting Guide to resolve the problem.
To access the Troubleshooting Guide, click on the Start button, then click on Help.
Troubleshooting should be listed in the table of contents.
- If one is included by the manufacturer of the SCSI controller, install a SCSI diagnostics program
such as Adaptec EZ-SCSI Lite.
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