The SCSI ABIOS provides support for two new device types:
Functions for this device ID control the SCSI adapter, and some of them also affect all devices attached to the adapter.
Functions for this device ID control the devices attached to the SCSI adapter.
Some functions affect all devices attached to the adapter, and others are
used to control a specific device via its logical ID.
These device types are intended for access to SCSI devices other than disk drives. Examples of these generic types are CD-ROMs, tape devices and communication devices, all of which may theoretically use the SCSI bus, provided the device is designed to do so.
The logical IDs for a particular peripheral type are allocated/deallocated to specific SCSI devices on demand via the allocate and deallocate function. Through the allocate function the device driver specifies a SCSI peripheral type, a removable media indicator and a relative unit number. If the device exists and is unallocated, ABIOS assigns that device to the logical ID. The controlling program can then use the logical ID to make requests through the SCSI adapter.