NAME

tk - TMSCP - TK50 single density magtape interface
             TU81 1600/6250 BPI magtape interface

DESCRIPTION

Each tk file (also known as TMSCP - Tape Mass Storage Control Protocol) magtape controller supports a single TK50/TU81 tape drive

When opened for reading or writing, the tape is not rewound.  When closed, it is rewound (unless the 0200 bit is on, see below).  If the tape was open for writing, a double end-of-file is written.  If the tape is not to be rewound the tape is backspaced to just between the two tapemarks. 

A standard tape consists of a series of 1024 byte records terminated by a double 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 last octal digit of the minor device number selects the drive.  The middle digit selects a controller.  The initial digit is even to select 6250 BPI, odd to select 1600 BPI for TU81.  If the 0200 bit is on (initial digit 2 or 3), the tape is not rewound on close.  Note that the minor device number has no necessary connection with the file name. 

Refer to the ULTRIX-11 System Management Guide for more information about logical device names. 

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 may be named rtk0 through rtk7 but the same minor-device considerations as for the regular files still apply. 

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.  A zero count is returned when a tape mark is read; another read will fetch the first record of the next tape file. 

RESTRICTIONS

For TU81s, changing the density is allowed only at BOT. 

FILES

/dev/tk#, /dev/rtk#, /dev/nrtk#
/dev/ht#, /dev/rht#, /dev/nrht#
/dev/gt#, /dev/rgt#, /dev/nrgt#

SEE ALSO

ULTRIX-11 System Management Guide
ULTRIX-11 Software Technical Description