Apple Power Macintosh 4400 - Manual (Page 51)

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. Make sure that no external SCSI device other than the
last one has a terminator.
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.)
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 a 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 Chapter 9 of this manual.)
External SCSI terminator
51 Connecting Equipment and Expanding Your Computer