Apple Macintosh 6500 - Manual (Page 60)

Terminate the SCSI chain properly
To ensure accurate transmission of information, a terminator must be at
each end of a SCSI chain. There is a built-in terminator at the beginning
of the chain. You need to make sure that the last device in the chain has a
terminator.
IMPORTANT In most cases, only the first and last devices in the SCSI chain
should be terminated (but see the exceptions, below). Make sure that no
external SCSI device other than the last one has a terminator.
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 II of this manual.)
To terminate the last device in the chain:
m If your SCSI device has a built-in terminator, use it 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.)
External SCSI terminator
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