Dell OptiPlex GXi Reference and Installation Guide ( - Page 89

SCSI ID Numbers Each device attached to a SCSI host adapter card, as well as the card itself, must have a unique SCSI identification (SCSI ID) number from 0 to 7. When SCSI devices are shipped from Dell, the default SCSI ID numbers are assigned as follows: • A SCSI host adapter card is configured as SCSI ID 7. • A SCSI tape drive or digital audio tape (DAT) drive is configured as SCSI ID 6. • A SCSI CD-ROM drive is configured as SCSI ID 5. • SCSI hard-disk drives are usually configured as SCSI ID 0. (The drive used to boot your system should always be configured as SCSI ID 0.) NOTE: There is no requirement that SCSI ID numbers be assigned sequentially or that devices be attached to the cable in order by ID number. SCSI Cable and SCSI Termination The type of cabling you receive with your SCSI device depends on the type of device you are installing. • If you are installing an internal narrow SCSI device (such as a CD-ROM drive or tape drive), you have a 50-pin internal SCSI cable as shown in Figure 7-14. One end of this cable attaches to the SCSI host adapter. The three connectors on the other end of the cable are used for attaching up to three narrow SCSI devices installed in the externally accessible drive bays. 50-pin SCSI cable (to device in externally accessible drive bay) • If you are installing an internal wide SCSI device (such as a wide SCSI hard-disk drive), you have a 68-pin internal SCSI cable as shown in Figure 7-14. One end of this cable attaches to the SCSI host adapter and the two connectors on the other end of the cable are used for attaching up to two SCSI harddisk drives installed in the hard-disk drive bracket. • If you are installing an external SCSI device, you have a shielded external cable that connects to the external SCSI connector on the SCSI host adapter card. You have a separate power cable to connect the SCSI device to an alternating current (AC) power source. Before installing SCSI devices in your computer, you must configure the termination on your SCSI device(s) to conform to the guidelines shown in Table 7-1. In Table 7-1, the term "last device" refers to the device attached to the end connector on the corresponding SCSI cable. For instructions on enabling and disabling termination, see the documentation for your SCSI host adapter card. CAUTION: Do not connect devices to all three connectors (internal narrow connector, internal wide connector, and external connector) on a single SCSI host adapter card. Such a configuration is a violation of the SCSI specification. You can safely connect devices to any two of these three connectors on a single SCSI host adapter card. 68-pin SCSI cable (to hard-disk drive) Figure 7-14. Internal SCSI Cable Installing Drives 7-11