MARC 21 Specifications for Record Structure, Character Sets, and Exchange Media
The use of an exchange medium (e.g., electronic, diskette, tape) is an integral part of
sharing files of MARC 21 records. This section includes media format and labeling
specifications for electronic file transfer (Part 1), microcomputer diskettes (Part 2), and magnetic
tape (Parts 3 and 4) which are being used to exchange MARC 21 data. The specifications vary
slightly for each medium to allow better utilization of the technology involved. Adherence to
media format and labeling specifications is essential for successful exchange of MARC 21
The following terms with these specialized definitions are used in the exchange media
Italicized terms within definitions are terms for which definitions are also
A file on the exchange
(e.g., diskette) that contains
records. When generally used, the term can refer to MARC records containing
bibliographic, classification, community information, and holdings data.
ASCII character 20(hex). Also referred to as the space character.
A collection of contiguously
characters written or read
a unit. Blocks are separated by an interblock gap. A block
one or more complete records, or it may contain segments of
segmented records. A block does not contain multiple segments
A record contained in a
file in which each block may contain more than
record or record segment.
A defined unit of
A physical exchange medium usually composed of a thin disk with a magnetic surface on both
sides, enclosed in protective case. A variety of diskette sizes exist, 5.25 inches or 3.5 inches
in diameter being the most common. Hardware to read from and write to such diskettes usually
support various densities of encoded data.
A defined character string that
contain one or more data elements.
A set of related records treated as a unit.
A file may form part of a physical or logical volume.
That part of a file that is recorded
on any one volume. The sections of a file do not have sections of other files
file transfer protocol (FTP).
technique and syntax for
communicating machine-readable data electronically in separate files without losing
data or file
of tape separating blocks of information.
A record at
the beginning of a volume, and at the beginning and end of a file
that identifies and characterizes that volume and file section. A label is not
considered to be part
a file section. A label is identified by a three letter Label Identifier followed
by a single character,
Label Number. Each label is recorded in a separate block.
an exchange medium that
identifies and characterizes the content of the file(s) and/or
One or more contiguous label
One or more contiguous labels with
the same three initial characters (Label Identifier).
processing system that writes files of MARC records for the purpose of data
interchange with a
system that is intended to
files of MARC records that have been processed by an originating
system for the purpose of data interchange.
Related pieces of data treated as
That part of a segmented
that is contained in any one block. The segments of a record do not have
segment control word (SCW).
string used to indicate the
type and content of a segment in a file of segmented
A record contained in a
file in which each record consists of a sequence of one or
more record segments. Records are contained in one or more consecutive
blocks, such that only one segment of each record can appear in any
A physical exchange medium usually
composed of a thin acetate
in a variety of widths (2-inch (5.08cm), 1-inch (2.54cm), and 1/2-inch (1.27cm) tape
are the most
common). The acetate film can be housed on reels or in cartridges.
A special control block
on magnetic tape to serve
a separator between file sections and label
groups and also between certain label groups.
A single operation in which
or set of volumes of MARC file(s) is transferred from an originating
system to a receiving
A physical or logical unit which
includes part of a file, a complete file, or more than one file. For separate
(e.g., a reel of magnetic tape), a volume is usually a single physical unit. A
label file(s) and one or more bibliographic
may contain sections of files but does not contain multiple sections of the same
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