1HT(4) Kernel Interfaces Manual HT(4)
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6 ht - RH-11/TU-16 magtape interface
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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.
14 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.
21 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'.
28 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.
35 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.
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46 /dev/mt?, /dev/rmt?
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49 tp(1)
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52 The magtape system is supposed to be able to take 64 drives. Such
53 addressing has never been tried.
54 Taking a drive off line, or running off the end of tape, while writing
56 have been known to hang the system.
57 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.
61 HT(4)