tm(4) [v7 man page]

TM(4)							     Kernel Interfaces Manual							     TM(4)

NAME

       tm - TM-11/TU-10 magtape interface

DESCRIPTION

       The  files mt0, ..., mt7 refer to the DEC TU10/TM11 magtape.  When closed it can be rewound or not, see below.  If it was open for writing,
       two end-of-files are written.  If the tape is not to be rewound it is positioned with the head between the two tapemarks.

       If the 0200 bit is on in the minor device number the tape is not rewound when closed.

       A standard tape consists of a series of 512 byte records terminated by an end-of-file.  To the extent possible, the system makes it  possi-
       ble, 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 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
       are named rmt0, ..., rmt7.  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 byte count is returned when a tape mark is read, but another read will fetch the first record of the new
       tape file.

FILES

       /dev/mt?, /dev/rmt?

SEE ALSO

       tp(1)

BUGS

       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.

																	     TM(4)

MTIO(4) 						   BSD Kernel Interfaces Manual 						   MTIO(4)

NAME

     mtio -- generic magnetic tape I/O interface

SYNOPSIS

     #include <sys/ioctl.h>
     #include <sys/types.h>
     #include <sys/mtio.h>

DESCRIPTION

     Magnetic tape has been the computer system backup and data transfer medium of choice for decades, because it has historically been cheaper in
     cost per bit stored, and the formats have been designed for portability and storage.  However, tape drives have generally been the slowest
     mass storage devices attached to any computer system.

     Magnetic tape comes in a wide variety of formats, from classic 9-track, through various Quarter Inch Cartridge (QIC) variants, to more modern
     systems using 8mm video tape, and Digital Audio Tape (DAT).  There have also been a variety of proprietary tape systems, including DECtape,
     and IBM 3480.

   UNIX TAPE I/O
     Regardless of the specific characteristics of the particular tape transport mechanism (tape drive), UNIX tape I/O has two interfaces: "block"
     and "raw".  I/O through the block interface of a tape device is similar to I/O through the block special device for a disk driver: the indi-
     vidual read(2) and write(2) calls can be done in any amount of bytes, but all data is buffered through the system buffer cache, and I/O to
     the device is done in 1024 byte sized blocks.  This limitation is sufficiently restrictive that the block interface to tape devices is rarely
     used.

     The "raw" interface differs in that all I/O can be done in arbitrary sized blocks, within the limitations for the specific device and device
     driver, and all I/O is synchronous.  This is the most flexible interface, but since there is very little that is handled automatically by the
     kernel, user programs must implement specific magnetic tape handling routines, which puts the onus of correctness on the application program-
     mer.

   DEVICE NAME CONVENTIONS
     Each magnetic tape subsystem has a couple of special devices associated with it.

     The block device is usually named for the driver, e.g.  /dev/st0 for unit zero of a st(4) SCSI tape drive.

     The raw device name is the block device name with an "r" prepended, e.g.  /dev/rst0.

     By default, the tape driver will rewind the tape drive when the device is closed.	To make it possible for multiple program invocations to
     sequentially write multiple files on the same tape, a "no rewind on close" device is provided, denoted by the letter "n" prepended to the
     name of the device, e.g.  /dev/nst0, /dev/nrst0.

     The mt(1) command can be used to explicitly rewind, or otherwise position a tape at a particular point with the no-rewind device.

   FILE MARK HANDLING
     Two end-of-file (EOF) markers mark the end of a tape (EOT), and one end-of-file marker marks the end of a tape file.

     By default, the tape driver will write two End Of File (EOF) marks and rewind the tape when the device is closed after the last write.

     If the tape is not to be rewound it is positioned with the head in between the two tape marks, where the next write will over write the sec-
     ond end-of-file marker.

     All of the magnetic tape devices may be manipulated with the mt(1) command.

     A number of ioctl(2) operations are available on raw magnetic tape.  Please see <sys/mtio.h> for their definitions.

     The manual pages for specific tape device drivers should list their particular capabilities and limitations.

SEE ALSO

     dd(1), mt(1), pax(1), tar(1), st(4), wt(4)

HISTORY

     The mtio manual appeared in 4.2BSD.

BUGS

     The status should be returned in a device independent format.

     If and when NetBSD is updated to deal with non-512 byte per sector disk media through the system buffer cache, perhaps a more sane tape
     interface can be implemented.

BSD
								 January 14, 1999							       BSD