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TM(4)                      Kernel Interfaces Manual                      TM(4)



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

DESCRIPTION
       The  files  mt0,  ...,  mt7  refer  to the DEC TU10/TM11 magtape.  When
       closed it can be rewound or not, see below.  If it was open  for  writ-
       ing, two end-of-files are written.  If the tape is not to be rewound it
       is positioned with the head between the two tapemarks.

       If the 0200 bit is on in the  minor  device  number  the  tape  is  not
       rewound when closed.

       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
       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.  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  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.



                                                                         TM(4)