PWB1/usr/man/man4/ht.4

.th HT IV 5/31/77
.sh NAME
ht \*- TU16 magtape interface
.sh DESCRIPTION
The files
.it "mt0, ..., mt15"
refer to the Digital Equipment Corporation TU16 magnetic tape control and transports.
The files
.it "mt0, ..., mt7"
are 800bpi, and the files
.it "mt8, ..., mt15"
are 1600bpi.
The files
.it "mt0, ..., mt3, mt8, ..., mt11"
are designated normal-rewind on close, and the files
.it "mt4, ..., mt7, mt12, ..., mt15"
are no-rewind on close.
When opened for reading or writing, the tape is assumed to
be positioned as desired.
When a file is closed, a double end-of-file (double tape mark)
is written if the file was opened for writing.
If the file was normal-rewind, the tape is rewound.
If it is no-rewind and the file was open for writing,
the tape is positioned before the second EOF just written.
If the file was no-rewind and opened read-only, the tape is
positioned after the EOF following the data just read.
Once opened, reading is restricted to
between the position when opened and the next EOF or
the last write.
The EOF is returned as a zero-length read.
By judiciously choosing
.it mt
files, it is possible to read and write multi-file tapes.
.s3
A standard tape consists of
several 512 byte records terminated by an EOF.
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 (although very inadvisable).
.s3
The
.it mt
files discussed above are 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 files are named
.it "rmt0, ..., rmt15."
Each
.it read
or
.it write
call reads or writes the next 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,
up to the buffer size specified.
In raw tape I/O, the buffer must begin on a word boundary
and the count must be even.
Seeks are ignored.
An EOF is returned as a zero-length read, with the tape positioned
after the EOF, so that the next read will return the next
record.
.sh FILES
/dev/mt*,
/dev/rmt*
.sh "SEE ALSO"
tp(I)
.sh BUGS
If any non-data error is encountered, it refuses to do anything
more until closed.
The driver is limited to four transports.