Interdata_v6/usr/doc/man/man4/mt.4

.th MT IV
.sh NAME
mt - magnetic tape drive
.sh DESCRIPTION
The file
.it mt0
refers to the 800-bpi magnetic tape drive.
The tape is automatically rewound when closed;
if the last operation was a write, two filemarks are written first.

A standard tape consists of a series of 512-byte records terminated by
a filemark.
To the extent possible, the system makes it possible, if inefficient,
to treat the tape like any other file.
Seeks have their usual meaning, and it is possible to read or write a byte
at a time.
Writing in very small units is inadvisable, however,
because it tends to create monstrous record gaps.

The interface discussed above is useful when it is desired to access the
tape in a way compatible with ordinary files.
When foreign tapes are to be dealt with,
and especially when long records are to be read or written,
the "raw" interface is appropriate.
The associated raw tape file is named
.it rmt0.
Each read or write call reads or writes the next sequential record on
the tape.
In the write case the record has the same length as the buffer given.
During a read, the record size is passed back as the number of bytes
read, provided it is no greater than the buffer size;
if the record is long, an I/O error is indicated.
In raw tape I/o, the buffer must begin on a halfword boundary and
the count must be even.
Seeks are ignored.
End-of-file status is returned when a tape mark is read
(or when the end of the tape is reached)
but another read will fetch the first record of the next tape file.

The files
.it mmt0
and
.it rmmt0
are identical to the corresponding
.it mt
files, but are not rewound automatically; they may be used to access
a tape containing multiple files.
Tape positioning operations are performed on an open
.it rmmt
file by a
.it stty
call. The first word of the parameter list is one of the following:
.in +4
.nf
0 - forward space file
1 - back space file
3 - write filemark
4 - forward space record
5 - back space record
7 - rewind
.in -4
.fi
The second and third words must be\ 0.
(These operations are also performed by the
.it tc
command.)
.sh FILES
/dev/mt0, /dev/mmt0
.br
/dev/rmt0, /dev/rmmt0
.sh "SEE ALSO"
tc(I), tm(I), tp(I)
.sh BUGS
A rewind or backspace operation from loadpoint will hang up the controller.
This condition must be cleared manually by a reset-forward-reset-online
sequence.

An attempt to write to a tape without a write ring will also hang up the
controller.
This must be cleared manually by a reset-online sequence.

A
.it gtty
call should be provided to return the status of the drive.