ct —
CS/80 cartridge tape interface
The cartridge tape interface as found in the 7946 and 9144 products provides a
  standard tape drive interface as described in
  mtio(4) with the following
  exceptions:
  - There is only one density.
- Only the “raw” interface is supported.
- The MTIOCTOPioctl(2) is limited. In
      particular, the command,MTFSRis not
    supported.
- The MTIOCGETioctl(2) is not
    supported.
- The record size for read and write operations must be between 1K and 64K
      inclusive.
Special files rct0 through
    rct3 refer to rewind on close interfaces to drives 0
    to 3. Files rct4 through
    rct7 refer to no-rewind interfaces. Files
    rct8 through rct11 refer to
    streaming rewind on close interfaces. (Only 9144 type devices can stream.)
    Lastly, rct12 through rct15
    refer to streaming no-rewind interfaces.
Read and writes of less than 1024 bytes will not behave as expected.