1HT(4)                      Kernel Interfaces Manual                      HT(4)


6       ht - RH-11/TU-16 magtape interface


9       The  files  mt0,  mt1,  ...  refer to the DEC RH/TM/TU16 magtape.  When
10       opened for reading or writing, the tape is not rewound.   When  closed,
11       it  is rewound (unless the 0200 bit is on, see below).  If the tape was
12       open for writing, a double end-of-file is written.  If the tape is  not
13       to be rewound the tape is backspaced to just between the two tapemarks.
15       A  standard tape consists of a series of 512 byte records terminated by
16       a double end-of-file.  To the extent possible, the system makes it pos‐
17       sible,  if  inefficient,  to treat the tape like any other file.  Seeks
18       have their usual meaning and it is possible to read or write a byte  at
19       a  time.   Writing in very small units is inadvisable, however, because
20       it tends to create monstrous record gaps.
22       The last octal digit of the minor device number selects the drive.  The
23       middle digit selects a controller.  The initial digit is even to select
24       800 BPI, odd to select 1600 BPI.  If the 0200 bit is on (initial  digit
25       2  or 3), the tape is not rewound on close.  Note that the minor device
26       number has no necessary connection with the  file  name,  and  in  fact
27       tp(1) turns the short name x into `/dev/mtx'.
29       The  mt  files  discussed above are useful when it is desired to access
30       the tape in a way compatible with ordinary files.  When  foreign  tapes
31       are  to  be dealt with, and especially when long records are to be read
32       or written, the `raw' interface is appropriate.  The  associated  files
33       may  be named rmt0, ..., rmt7, but the same minor-device considerations
34       as for the regular files still apply.
36       Each read or write call reads or writes the next record  on  the  tape.
37       In  the  write case the record has the same length as the buffer given.
38       During a read, the record size is passed back as the  number  of  bytes
39       read,  provided it is no greater than the buffer size; if the record is
40       long, an error is indicated.  In raw tape I/O, the buffer must begin on
41       a word boundary and the count must be even.  Seeks are ignored.  A zero
42       count is returned when a tape mark is read; another read will fetch the
43       first record of the next tape file.


46       /dev/mt?, /dev/rmt?


49       tp(1)


52       The  magtape  system  is  supposed  to be able to take 64 drives.  Such
53       addressing has never been tried.
55       Taking a drive off line, or running off the end of tape, while  writing
56       have been known to hang the system.
58       If  any  non-data  error is encountered, it refuses to do anything more
59       until closed.  In raw I/O, there should be a way to perform forward and
60       backward record and file spacing and to write an EOF mark explicitly.
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