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Annotation of 41BSD/sys/newsys/tm.4, revision 1.1.1.1

1.1       root        1: .TH HT 4 
                      2: .SH NAME
                      3: ht \- RH-11/TE-16 magtape interface
                      4: .SH DESCRIPTION
                      5: The files
                      6: .I "mt0, ..., mt15"
                      7: refer to the DEC RH/TM/TE-16 magtape.
                      8: Even numbered files are 800 bpi, and odd numbered
                      9: files are 1600bpi.
                     10: The files
                     11: .I "mt0, ..., mt15"
                     12: are rewound when closed; the files
                     13: .I "nmt0, ... nmt15"
                     14: are not.
                     15: When a file open for writing is closed, a double end-of-file is written.
                     16: .PP
                     17: A standard tape consists of a
                     18: series of 512 byte records terminated by an
                     19: end-of-file.
                     20: To the extent possible, the system makes
                     21: it possible, if inefficient, to treat
                     22: the tape like any other file.
                     23: Seeks have their usual meaning and it is possible
                     24: to read or write a byte at a time.
                     25: Writing in very small units is inadvisable,
                     26: however, because it tends to create monstrous record
                     27: gaps.
                     28: .PP
                     29: The
                     30: .I mt
                     31: files discussed above are useful
                     32: when it is desired to access the tape in a way
                     33: compatible with ordinary files.
                     34: When foreign tapes are to be dealt with, and especially
                     35: when long records are to be read or written, the
                     36: `raw' interface is appropriate.
                     37: The associated files are named
                     38: .I "rmt0, ..., rmt15,"
                     39: and
                     40: .I "nrmt0, ..., nrmt15."
                     41: .PP
                     42: Each
                     43: .I read
                     44: or
                     45: .I write
                     46: call reads or writes the next record on the tape.
                     47: In the write case the record has the same length as the
                     48: buffer given.
                     49: During a read, the record size is passed
                     50: back as the number of bytes read, provided it is no greater
                     51: than the buffer size;
                     52: if the record is long, an error is indicated.
                     53: In raw tape I/O, the buffer must begin on a word boundary
                     54: and the count must be even.
                     55: Seeks are ignored.
                     56: A zero count is returned when a tape mark is read;
                     57: another read will fetch the first record of the
                     58: next tape file.
                     59: .PP
                     60: In raw mode, the 
                     61: .I ioctl
                     62: system call can be used to access device special functions.
                     63: This call takes the form:
                     64: .I "ioctrl(fdes, code, count)."
                     65: Codes are defined in 
                     66: .I "<sys/mt.h>,"
                     67: and consist of:
                     68: .in +8
                     69: .ti -3
                     70: SKIPF: Skip blocks, forward direction
                     71: .ti -3
                     72: SKIPR: Skip blocks, reverse direction
                     73: .ti -3
                     74: WEOF: Write EOF
                     75: .ti -3
                     76: REW: Rewind
                     77: .ti -3
                     78: SKIPFF: Skip one or more EOF's (skip forward file)
                     79: .ti -3
                     80: SKIPRF: Skip EOF marks or to BOT, reverse direction
                     81: .in -8
                     82: The
                     83: .I count
                     84: argument must be positive, and specifies the number of times
                     85: the selected operation is to be repeated.
                     86: .SH FILES
                     87: /dev/mt?,
                     88: /dev/rmt?
                     89: .SH "SEE ALSO"
                     90: tp(1)
                     91: .SH BUGS
                     92: The magtape system is supposed to be able
                     93: to take 64 drives.
                     94: Such addressing has never been tried.
                     95: These bugs will be fixed when
                     96: we get more experience with this device.
                     97: .PP
                     98: The driver is limited to four transports.
                     99: .PP
                    100: If any non-data error is encountered, it refuses to do anything
                    101: more until closed.

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