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Annotation of coherent/a/usr/man/COHERENT/tape, revision 1.1

1.1     ! root        1: 
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        !             3: tape                      Device Driver                      tape
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        !             8: Magnetic tape devices
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        !            10: 
        !            11: This section gives a general explanation of COHERENT's use of in-
        !            12: dustry-standard half-inch,  nine-track magnetic tape.  Exceptions
        !            13: or additional information may be found in sections of this manual
        !            14: describing particular devices.
        !            15: 
        !            16: A  tape volume  contains files,  each consisting  of one  or more
        !            17: records and terminated by  a tape mark.  Two tape marks terminate
        !            18: the  last file.   Tape  records may  vary in  length, but  cannot
        !            19: exceed 2^16 bytes (2^15 is more practical).
        !            20: 
        !            21: Like  other block-oriented  devices, tape  units may  be accessed
        !            22: through the  system's cooked interface or  through the raw inter-
        !            23: face.  On a cooked device, seeking to any byte offset and reading
        !            24: in any number  of bytes is possible.  It is  not possible to read
        !            25: beyond the tape mark at the end of the current file.  All records
        !            26: in the file  must be 512 bytes long, except  the last.  Write re-
        !            27: quests must be made in  increments of 512 bytes, except the last.
        !            28: A cooked tape may be mounted like a disk, but only as a read-only
        !            29: file system.
        !            30: 
        !            31: A raw device bypasses the buffer cache, so I/O occurs directly to
        !            32: or from the user's  buffer.  One write request generates one tape
        !            33: record,  and one  read request returns  exactly one  record.  The
        !            34: number of bytes read may be less than expected.  If the tape mark
        !            35: is read,  a count of  zero is returned, but  the system positions
        !            36: the tape  at the start of  the next tape file.   Seeking on a raw
        !            37: device is ignored, and mounting is not allowed.
        !            38: 
        !            39: A unit cannot be opened if  it is off-line or already in use.  If
        !            40: the write ring is absent,  the unit cannot be opened for writing.
        !            41: Closing the  device has varying  effects, depending on  the minor
        !            42: device opened  and whether the  device was opened  for reading or
        !            43: writing.  In the case of reading, the tape is rewound; if the no-
        !            44: rewind option was specified,  the tape advances to the next file.
        !            45: In the case of writing, two tape marks are written at the current
        !            46: position and  the tape  is rewound;  if the no-rewind  option was
        !            47: specified, two tape marks  are written and the tape is positioned
        !            48: between them.   When you close a device that  had been opened for
        !            49: writing,  the tape  volume  ends at  the  current position;  data
        !            50: beyond this point are undefined.
        !            51: 
        !            52: The following  device options exist, selected  by prefixes to the
        !            53: device name:
        !            54: 
        !            55: hh     Read or  write  data at  high density.   The exact  density
        !            56:      depends on the drive model,  but 1600 BPI (high) and 800 BPI
        !            57:      (low) are typical.
        !            58: 
        !            59: nn    Do not rewind on close.
        !            60: 
        !            61: 
        !            62: 
        !            63: 
        !            64: COHERENT Lexicon                                           Page 1
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        !            68: 
        !            69: tape                      Device Driver                      tape
        !            70: 
        !            71: 
        !            72: 
        !            73: rr    The device is raw.
        !            74: 
        !            75: Hard errors may occur during tape operation.  They include detec-
        !            76: tion of the  end-of-tape (EOT) reflector, reading an unexpectedly
        !            77: long record, or seeking a cooked tape into a tape mark.  After an
        !            78: error, no  further operations may be performed  on the unit until
        !            79: the program closes the  device and the operator rewinds the tape.
        !            80: Soft parity errors may arise  due to dirt, bad tape or misaligned
        !            81: heads.  On  writes, the driver attempts to  place the record fur-
        !            82: ther along  the tape.   On reads,  the driver simply  rescans the
        !            83: record.  After several  failures, the driver announces a hard er-
        !            84: ror.
        !            85: 
        !            86: Most utilities  use generic device names, which  are links to the
        !            87: actual device files appropriate for the site.
        !            88: 
        !            89: ***** Files *****
        !            90: 
        !            91: /ddeevv/mmtt -- Generic cooked tape device
        !            92: /ddeevv/rrmmtt -- Generic raw tape device
        !            93: 
        !            94: ***** See Also *****
        !            95: 
        !            96: device drivers
        !            97: 
        !            98: ***** Diagnostics *****
        !            99: 
        !           100: Drivers may report errors to the console.
        !           101: 
        !           102: ***** Notes *****
        !           103: 
        !           104: Not every edition of COHERENT supports magnetic tape.
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        !           130: COHERENT Lexicon                                           Page 2
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