Technical data

mtio(7I) Ioctl Requests SunOS 5.5
NAME mtio − general magnetic tape interface
SYNOPSIS #include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/mtio.h>
DESCRIPTION 1/2”, 1/4”, 4mm, and 8mm magnetic tape drives all share the same general character
device interface.
There are two types of tape records: data records and end-of-file (EOF) records. EOF
records are also known as tape marks and file marks. A record is separated by inter-
record (or tape) gaps on a tape.
End-of-recorded-media (EOM) is indicated by two EOF marks on 1/2” tape; by one on
1/4”, 4mm, and 8mm cartridge tapes.
1/2” Reel Tape Data bytes are recorded in parallel onto the 9-track tape. Since it is a variable-length tape
device, the number of bytes in a physical record may vary.
The recording formats available (check specific tape drive) are 800BPI, 1600 BPI, 6250BPI,
and data compression. Actual storage capacity is a function of the recording format and
the lengthof the tape reel. For example, using a 2400 foot tape, 20 Mbyte can be stored
using 800BPI, 40 Mbyte using 1600BPI, 140 Mbyte using 6250 BPI, or up to 700 Mbyte
using data compression.
1/4” Cartridge Tape Data is recorded serially onto 1/4” cartridge tape. The number of bytes per record is
determined by the physical record size of the device. The I/O request size must be a
multiple of the physical record size of the device. For QIC-11, QIC-24, andQIC-150 tape
drives, the block size is 512 bytes.
The records are recorded on tracks in a serpentine motion. As one track is completed, the
drive switches to the next and begins writing in the opposite direction, eliminating the
wasted motion of rewinding. Each file, including the last, ends with one file mark.
Storage capacity is based on the number of tracks the drive is capable of recording. For
example, 4-track drives can only record 20 Mbyte of data on a 450 foot tape; 9-track
drives can record up to 45 Mbyte of data on a tape of the same length. QIC-11 is the only
tape format available for 4-track tape drives. In contrast, 9-track tape drives can use
eitherQIC-24 or QIC-11. Storage capacity is not appreciably affected by using either for-
mat. QIC-24 is preferable toQIC-11 because it records a reference signal to mark the posi-
tion of the first track on the tape, and each block has a unique block number.
The QIC-150 tape drives require DC-6150 (or equivalent) tape cartridges for writing.
However, they can read other tape cartridges in QIC-11, QIC-24, or QIC-120 tape formats.
8mm Cartridge Tape Data is recorded serially onto 8mm helical scan cartridge tape. Since it is a variable-
length tape device, the number of bytes in a physical record may vary. The recording for-
mats available (check specific tape drive) are standard 2Gbyte, 5Gbyte, and compressed
format.
7I-216 modified 30 Aug 1995