Technical data

Managing Storage Media
9.1 Understanding Storage Media Concepts
Table 9–6 (Cont.) Terms Related to Magnetic Tapes
Term Definition
bpi Bits per inch; measure used for characters of data on tape on OpenVMS systems.
Also called density.
IRG Interrecord gap; interval of space between blocks.
Record blocking Grouping of individual records into a block, thereby reducing wasted space.
Sequential Organization of magnetic tape data; that is, data is organized in the order in which
it is written to the tape.
Magnetic Tape
Ancillary Control
Process (MTACP)
Internal software process that interprets the logical format of standard labeled
volumes.
Beginning-of-tape
(BOT) marker and
end-of-tape (EOT)
marker
Pieces of photoreflective tape that appear on every volume to delimit the writable
area on the volume.
ANSI standards require that a minimum of 14 feet to a maximum of 18 feet of
magnetic tape precede the BOT marker; a minimum of 25 feet to a maximum of 30
feet of tape, of which 10 feet must be writable, must follow the EOT marker.
The EOT marker indicates the start of the end of the writable area of the tape,
rather than the physical end of the tape. Therefore, data and labels can be written
after the EOT marker.
Data record
storage
Within tape files, data records are stored in variable-size data blocks. Each block
contains one or more records. RMS provides management of records.
Header labels Set of labels that the tape file system writes on the tape immediately preceding the
data blocks when you create a file on tape. These labels contain information such
as the user-supplied file name, creation date, and expiration date. To access a file
on magnetic tape by the file name, the file system searches the tape for the header
label set that contains the specified file name.
Trailer labels Set of labels that the tape file system writes on the tape following the file.
Multivolume file Additional volume on which a file is continued when the data blocks of a file or
related files do not physically fit on one volume (a reel of magnetic tape).
Volume set The volumes on which a set of files is recorded.
9.1.3.1 Record Blocking
Figure 9–2 shows how record blocking can save space.
Managing Storage Media 9–11