The
sd driver provides support for SCSI bus and Advanced Technology Attachment Packet Interface (ATAPI) disks. It allows the disk to be divided up into a set of pseudo devices called
partitions. In general the interfaces are similar to those described by
wd(4).
Where the
wd(4) device has a fairly low level interface to the system, SCSI devices have a much higher level interface and talk to the system via a SCSI host adapter (e.g.,
ahc(4)). A SCSI adapter must also be separately configured into the system before a SCSI disk can be configured.
When the SCSI adapter is probed during boot, the SCSI bus is scanned for devices. Any devices found which answer as ‘
Direct' type devices will be attached to the
sd driver.
For the use of flags with ATAPI devices, see
wd(4).