Apple Power Macintosh 9600 - Manual (Page 87)

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, do one of the following:
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 authorized Apple 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.
External SCSI terminator
87 Connecting Additional Equipment