HT(IV) 2/9/75 HT(IV)
NAME
ht - RH-11/TU-16 magtape interface
DESCRIPTION
The files mt0, ..., mt7 refer to the DEC RH/TM/TU16 magtape.
When opened for reading or writing, the tape is rewound.
When closed, it is rewound; if it was open for writing, a
double end-of-file is written first.
A standard tape consists of a series of 512 byte records
terminated by a double end-of-file. 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 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
rmt0, ..., rmt7. Each read or 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,
provided it is no greater than the buffer size; if the
record is long, an error is indicated. In raw tape I/O, the
buffer must begin on a word boundary and the count must be
even. Seeks are ignored. An error is returned when a tape
mark is read, but another read will fetch the first record
of the new tape file.
FILES
/dev/mt?, /dev/rmt?
SEE ALSO
tp (I)
BUGS
Raw I/O doesnt work yet. The magtape system is supposed to
be able to take 64 drives. Such addressing has never been
tried. These bugs will be fixed when we get more experience
with this device.
If any non-data error is encountered, it refuses to do
anything more until closed. In raw I/O, there should be a
way to perform forward and backward record and file spacing
and to write an EOF mark.