NAME

ht − RH11/RH70 - TM02/3 magtape controller

DESCRIPTION

Each TM02/3 magtape controller supports up to eight TU16/TE16/TU77 tape drives.  Eight TM02/3 controllers may be connected to a single RH11 or RH70 massbus controller. 

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 1600 BPI, odd to select 800 BPI.  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 rmt0 through rmt7 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. 

FILES

/dev/mt?, /dev/rmt?, /dev/nrmt? 
/dev/ht?, /dev/rht?, /dev/nrht?

SEE ALSO

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

RESTRICTIONS

The magtape system is supposed to be able to take 64 drives.  Such addressing has never been tried. 

Taking a drive off line, or running off the end of tape while writing, has been known to hang the system. 

If any non-data error is encountered, it refuses to do anything more until closed.  In raw I/O, there should be a way to perform forward and backward record and file spacing and to write an EOF mark explicitly.