# 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.
continue/quit?
```

## See also

- [account-save command](https://d3codex.com/tcl/account-save-command/)
- [file-save command](https://d3codex.com/tcl/file-save-command/)
- [save command](https://d3codex.com/tcl/save-command/)
- [sp-assign command](https://d3codex.com/tcl/sp-assign-command/)
- [sreformat command](https://d3codex.com/access/sreformat-command/)
- [t-dump command](https://d3codex.com/tcl/t-dump-command/)
- [t-load command](https://d3codex.com/tcl/t-load-command/)
- [t-rdlbl command](https://d3codex.com/tcl/t-rdlbl-command/)
- [t-read command](https://d3codex.com/tcl/t-read-command/)
- [t-wtlbl command](https://d3codex.com/tcl/t-wtlbl-command/)

---
Source: https://d3codex.com/tcl/tape-devices-overview/ - part of the D3Codex reference.