4BSD/usr/man/cat4/ht.4

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



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

DESCRIPTION
     The files _m_t_0, ..., _m_t_1_5 refer to the DEC RH/TM/TE-16
     magtape.  The files _m_t_0, ..., _m_t_7 are 800 bpi, 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, a double end-of-file is
     written.

     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 may be 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 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.





Printed 11/10/80                                                1






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



     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 explicitly.



















































Printed 11/10/80                                                2