SCSI Devices

Small Computer Standard Interface (SCSI) is a multiple-device chained interface used in many devices such as hard disks and CD-ROM drives. Plug and Play SCSI devices support dynamic changes to the adapter and automatic configuration of device ID and termination.

Configuration of a SCSI device can be separated into two distinct processes:

• Configuring the SCSI bus itself, such as terminating both ends of the SCSI bus and setting device IDs.
• Configuring the SCSI host adapter, such as assigning an IRQ channel, DMA channel, and so on.

Configuring a SCSI bus that is not Plug and Play-compliant is difficult for most users. The list of issues related to configuring a SCSI bus is long, including:

• SCSI device ID assignment
• Termination
• SCSI parity
• Command sets
• Disk geometry and software

For example, the SCSI-2 specification does not define an automated ID assignment mechanism, so the user is responsible for making sure that no two SCSI devices on the same SCSI bus share the same SCSI ID. Also, you might replace a SCSI host adapter with one from another company and find it doesn't work due to differences in disk geometries or the way devices are mapped to INT 13 parameters.

For more information about support for SCSI devices and drivers, see Chapter 20, "Disks and File Systems."