| SS(4) | Device Drivers Manual | SS(4) | 
ss* at scsibus? target ? lun ?
The ss driver provides support for SCSI bus based
  document scanners.
  - /dev/ssu
- SCSI bus scanner unit u
- /dev/nssu
- SCSI bus scanner unit u - no rewind.
- /dev/enssu
- SCSI bus scanner unit u -
      ioctl(2) operations
    only.
Kenneth Stailey, Joachim Koenig
Only a limited number of HP Scanjet and Mustek scanners are supported. Other
  scanners can probably be accessed using the SCSI
  uk(4) driver instead.