HT(4)

NAME
ht - RH-11/TE-16 magtape interface

DESCRIPTION
The files mt0, ..., mt15 refer to the DEC RH/TM/TE-16 magtape. The files mt0, ..., mt7 are 800 bpi, and mt8, ..., mt15 are 1600bpi. The files mt0, ..., mt3 and mt8, ..., mt11 are rewound when closed; the others are not. When a file open for writing is closed, a double end-of-file is written.

A standard tape consists of a series of 512 byte records terminated by an 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 may be named rmt0, ..., rmt15, but the same minor-device considerations as for the regular files still apply.

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. A zero count is returned when a tape mark is read; another read will fetch the first record of the next tape file.

FILES
/dev/mt?, /dev/rmt?

SEE ALSO
tp(1)

BUGS
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.

The driver is limited to four transports.

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 explicitly.