See the instructions that came with each SCSI device for information on checking and setting
its SCSI ID number.
Important If you use two or more devices attached to the SCSI interface with the same ID
number, your computer will not start up properly, your equipment may malfunction, and you
may lose data as a result.
Use the Right Type and Length of Cable
To attach a SCSI device to your computer or to another device in the chain, always use SCSI
cables that are double-shielded, such as Apple SCSI cables. Never use printer-type RS-232
cables (commonly used with DOS and Windows computers).
Poor-quality SCSI cables are often the cause of SCSI problems. Avoid mixing brands and types
of SCSI cables.
If the device is the first or only one you’re connecting, use a SCSI system cable to connect it
to the computer’s SCSI port. If the device is not the first one, use a SCSI peripheral interface
cable to connect it to the last device in the chain.
Keep the cables between SCSI devices as short as possible. Cables 18 to 24 inches long are
best. PowerBooks and some SCSI devices (particularly scanners) may not be able to handle
cables longer than 24 inches.
Important The total length of the cables in a SCSI chain should not exceed 6 meters (about
20 feet). SCSI cables must have a 110-ohm impedance. For best results, use SCSI cables
manufactured by Apple Computer.
Terminate the SCSI Chain Properly
To ensure accurate transmission of information, a terminator must be present at each end of
a SCSI chain. When you connect external SCSI devices, make sure that only the last external
device in the chain has a terminator. (The second terminator at the beginning of the SCSI
chain is inside your computer.)
Important In almost all cases, only the first and last devices in the SCSI chain should be
terminated, with one exception noted later in this section. Make sure that no external SCSI
device but the last one has a terminator.
SCSI system cable SCSI peripheral interface cable
Using Your Macintosh and Connecting Additional Equipment 33