TM(IV)                       2/21/74                       TM(IV)


     tm - TM-11/TU-10 magtape interface


     The files mt0, ..., mt7 refer to the DEC TU10/TM11  magtape.

     When  opened  for  reading  or writing, the tape is rewound.

     When closed, it is rewound; if it was open for  writing,  an

     end-of-file is written first.

     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.  An error is returned when a  tape

     mark  is  read, but another read will fetch the first record

     of the new tape file.


     /dev/mt?, /dev/rmt?


     tp (I)


     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.