4BSD/usr/man/cat4/tm.4

TM(4)               UNIX Programmer's Manual                TM(4)



NAME
     tm - TM-11/TU-10 magtape interface

DESCRIPTION
     The files _m_t_0, ..., _m_t_1_5 refer to the DEC TU10/TM11 magtape.
     The files _m_t_0, ..., _m_t_8 are 800bpi, and _m_t_8, ..., _m_t_1_5 are
     1600bpi.  The files _m_t_0, ..., _m_t_3 and _m_t_8, ..., _m_t_1_1 are
     rewound when closed; the others are not.  When a file open
     for writing is closed, two end-of-files are written.  If the
     tape is not to be rewound it is positioned with the head
     between the two tapemarks.

     A standard tape consists of a series of 1024 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 _m_t 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 _r_m_t_0, ...,
     _r_m_t_1_5, but the same minor-device considerations as for the
     regular files still apply.

     Each _r_e_a_d or _w_r_i_t_e 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 byte count 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(1)

BUGS
     If any non-data error is encountered, it refuses to do any-
     thing 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.




Printed 11/10/80                                                1