Block count

The block count shown in the HDR1 label is always 0 (EBCDIC or BCDIC). This 0 is recorded in the data control block (in binary) and increased during processing for comparison to the block count shown in the trailer label (EOV1 or EOF1).

For reading backward, the block count shown in the trailer label (EOV1 or EOF1) is recorded in the data control block and decreased during processing for comparison to the 0 block count in the HDR1 label.

The block count is verified at end-of-data or end-of-volume. For more information, see Verifying block count and Verifying block count in label when reading.