If the LRECL and BLKSIZE fields are not specified in the DCB, the terminal line size default, or the line size the terminal user has specified using the TERMINAL command, is merged into the data control block fields as if it came from the label of the data set.

For BSAM, BLKSIZE is used by TSO/E to determine the length of the text line it is to process. For both BSAM and QSAM, if the text entered from the terminal is shorter than the value specified for LRECL, and if F format is used, blanks are supplied on the right. For either access technique, if the text entered is longer than BLKSIZE or LRECL, the next GET or READ retrieves the remainder of the message. If the record generated by the problem program is longer than the specified line size, multiple lines are displayed at the terminal.