Unless you specify otherwise, the system assigns a line number to each line as it is entered. The default is an interval of 10. Line numbers make editing much easier, because you can refer to each line by its own number.

Each line number consists of up to eight digits, with the significant digits justified on the right and preceded by zeros. Line numbers are placed at the beginning of variable-length records and at the end of fixed-length records. (Exception: Line numbers for COBOL fixed-length records are placed in the first six positions at the beginning of the record.) When you are working with a data set that has line numbers, you can have the new line number listed at the start of each new input line. If you are creating a data set without line numbers, you can request that a prompting character be displayed at the terminal before each line is entered. Otherwise, none is issued.

Input records are converted to uppercase characters, unless you specify the ASIS or TEXT operand. The TEXT operand also specifies that character-deleting indicators and tabulation characters are recognized, but all other characters are added to the data set unchanged.

All Assembler source data sets must consist of fixed-length records, 80 characters long. These records might not be line numbers. If the records are line-numbered, the number can be located anywhere within columns 73 to 80 of the stored record (the printed line number always appears at the left margin).