In Record I/O, file data is treated in terms of records. Record files are used with the READ, WRITE, REWRITE, and DELETE statements. Execution of one of these statements transmits one record to or from the file and updates the current position of the file.
A record is a contiguous set of bytes of data in the file. The records of the file may all be of the same fixed length, as specified when the file is created, or they may be of varying lengths. Certain files with variable-length records require that a maximum length be specified when the file is created.
The data bytes that comprise a record file may be ASCII characters, but they may also be any kind of binary data, including being paired as halfwords, grouped as binary fullwords or double words, grouped as packed-decimal strings, or considered as bit fields of any length.
Record files may be keyed or not. If a record file does not have keys, its records can be accessed only in sequential order as they exist in the file, one after the other from the beginning of the file to the end. Open PL/I supports two keyed access methods: indexed (VSAM) I/O, which is based on character-string keys, and relative record I/O, which is based on integer record numbers.