Adaptec 29320A-R User Guide - Page 24

Adaptec Ultra320 SCSI Cards User's Guide Understanding SCSI SCSI (pronounced "scuzzy") stands for Small Computer Systems Interface. SCSI is an industry standard computer interface for connecting SCSI devices (such as a hard disk drive, CD-ROM drive, or scanner) to a common SCSI bus. A SCSI bus is an electrical pathway that consists of a SCSI adapter card (such as the Adaptec SCSI Card) installed in a computer and one or more SCSI devices. SCSI cables are used to connect the devices to the SCSI adapter card. The Adaptec SCSI Card has up to two independent SCSI buses (channels). For the SCSI bus to function properly, a unique SCSI ID must be assigned to the SCSI card and each SCSI device connected to it, and the SCSI bus must be properly terminated. SCSI IDs Each device attached to the Adaptec SCSI Card, as well as the Adaptec SCSI Card itself, must be assigned a unique SCSI ID number from 0 to 15 for each of the two SCSI buses. A SCSI ID uniquely identifies each SCSI device on the SCSI bus and determines priority when two or more devices are trying to use the SCSI bus at the same time. Refer to the device's documentation to set the SCSI ID. Here are some general guidelines for SCSI IDs: s For internal SCSI devices, the SCSI ID usually is set by configuring a jumper on the device. s For external SCSI devices, the SCSI ID usually is set with a switch on the back of the device. s SCSI ID numbers do not need to be sequential, as long as the Adaptec SCSI Card and each device has a different number. For example, on each of the two SCSI buses you can have an internal SCSI device with ID 0, and an external SCSI device with ID 6. s SCSI ID 7 has the highest priority on the SCSI bus. The priority of the remaining IDs, in descending order, is 6 to 0, then 15 to 8. 1-8