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AP2500 Hardware Reference Guide
II. Components
II. System Components
Ultra2 SCSI Disk Drive
The Ultra2 SCSI disk drive has separate signal and power connections. The
power connector is the same as standard hard disk drive power. The signal
cable is different. For proper signal stability in Ultra2 speeds, a special twisted
ribbon cable must be used. Each pair of wires are twisted for signal shield-
ing like that of high speed (e.g. category 5) LAN cabling.
IMPORTANT:
You must use Ultra2 SCSI ribbon cables for Ultra2 devices.
Ultra2 ribbon cables (may be colored red and white) are similar to wide-
SCSI ribbon cables (normally colored gray) but each pair of wire is twisted
to reduce signal interference.
Ultra2 SCSI hard disk drive connections
Red stripe of signal cable
Red stripe of power cable
External Ultra2 SCSI Terminator
To prevent SCSI signal loss, the provided external SCSI terminator must be
used at the end of the 68-pin SCSI cable. 50-pin SCSI cables may also use
terminators but usually use termination jumpers on the device itself. Cur-
rently Wide-SCSI devices have termination jumpers but Ultra2 devices do
not. Some manufacturers ship SCSI devices with the terminator set, others
do not. All termination jumpers must be removed along the cable where the
external SCSI terminator is used.
