Adaptec USB2Xchange User Manual

Contents

24Understanding SCSIUnderstanding SCSISCSI (pronounced “scuzzy”) stands for Small Computer SystemInterface. SCSI is an industry standard computer interface forconnecting SCSI devices (such as a hard disk drive, CD-ROMdrive, or scanner) to a common SCSI bus.A SCSI bus is the path or channel that connects your computer,USB2Xchange adapter, and one or more SCSI devices. It's not aphysical object that you can point to; instead, it's the wholecollection of SCSI cables and devices (including the USB2Xchange)that make up the communication channel. The size of the busgrows when more devices are added. When there is activity on theSCSI bus, the LED on the top of your USB2Xchange flashes.For the SCSI bus to function properly, each SCSI device must have aunique SCSI ID and must be correctly terminated. For moreinformation, see the next section (Preparing SCSI Devices for Installation) .Preparing SCSI Devices for InstallationWhen preparing to install SCSI devices, make sure to: Check the SCSI IDs. Ensure that the USB2Xchange adapter andeach SCSI device you want to connect to it has a unique SCSIID. See the next section, SCSI IDs, for more information. Use only high-quality SCSI cables to ensure reliable datatransfer. See Using SCSI Cables on page 26 for more information. Terminate the ends of the SCSI bus. See Terminating the SCSIBus on page 25 for more information.SCSI IDsSCSI IDs identify each device on the SCSI bus and determinepriority when two or more devices are trying to use the SCSI bus atthe same time. The SCSI card is also identified by a SCSI ID. For theUSB2Xchange adapter, SCSI IDs are numbers between 0 and 7.Adaptec presets the USB2Xchange to SCSI ID 7. You cannot changethis setting. SCSI ID 7 has the highest priority on the SCSI bus; theremaining SCSI IDs descend in priority from 6 to 0.Use SCSI ID 0 for the first SCSI hard disk drive.