Technical information

Terminate the SCSI chain properly
To ensure accurate transmission of information, a terminator must be present at each end of a SCSI
chain. There is already a built-in terminator at the beginning of the chain. Therefore, you only need to
make sure that the last device in the chain has a terminator.
Important In almost all cases, only the first and last devices in the SCSI chain should be terminated
(with the exceptions noted below). Make sure that no external SCSI device but the last one has a
terminator.
To terminate the last device in the chain:
m Use a device that has a built-in terminator as the last device in the chain.
If you wish to attach two or more SCSI devices that have built-in terminators, an Apple-authorized
service provider can remove the extra built-in terminators.
m If the device at the end of the SCSI chain does not have a built-in terminator, attach an external
terminator. You can attach or remove external terminators yourself. (Do not use a black terminator;
the black terminators are for Macintosh IIfx computers and certain LaserWriter printers only.)
Terminators are available at Apple-authorized dealers.
Exceptions to the “first and last” rule: If the SCSI chain is 18 inches or shorter, the terminator on the
last device is not needed. If the total cable length in the chain is greater than 10 feet, the chain may
need a third terminator at the 10-foot point. Do not add the third terminator unless you are
experiencing a SCSI problem, and check all other possible causes of the problem before adding the
third terminator. (See the information on troubleshooting SCSI problems in Part V of this manual.)
External SCSI terminator
Connecting
Additional
Equipment
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