Tape devices overview

Tape devices are storage medium for reading and writing tapes.

Multiuser tape

A port attaches more than one device to itself and ports can independently access different tape devices simultaneously. This expands the functionality of t-det. It now requires a device number or else it detaches all tape devices held by the port. The t-det (u command releases a tape device on the system.

The t-att command is used primarily to change block sizes. The t-act command is available to switch between devices if more than one is attached to a single port. Remember, you can only issue one tape command at a time.

Tape label

Traditionally, D3 tapes have an identifying label written on the first 80 bytes of the tape. Labels contain up to 47 characters, depending on the length of the Timedate stamp and Platform ID

Tape        Element   Element
Position    Length    Description
--------    -------   ----------------------------------
01          01        Label Identifier. Always an "L".
02          01        (space)
03 - 06     04        Record Length (in hexadecimal)
                      "01F4" = 500-byte record
                      "03E8" = 1000-byte record
                      "4000" = 16384-byte record
07          01        (space)
08 - 15     08        System Time at time of tape-writing.
                      "00:00:00" format
16 - 17     02        (spaces)
18 - 28     11        System Date at time of tape-writing.
                      "mmm dd yyyy" format
29          01        (space)
30 - 77     48        Label Header Text.
78          01        (space)
79 - 80     02        Tape volume (reel) number.
--------    -------   ----------------------------------

If the tape is created:

  • by using the t-dump command, the label contains the source file name and text specified in the t-dump heading option (if any).

  • by a file-save, account-save, or save command, then it contains the word data, and optionally, the information entered at the file-save tape label: prompt.

  • as spooler output, the label contains the word spooler, and optionally, the account name and user-ID of the creator.

Note: If the device label size does not match the tape (media) label size, the prompt below displays. In the event of a mismatch, you are prompted on the first reel.
Device label size does not match tape label size.