The BSP macro backspaces one block on the magnetic tape or direct access volume being processed. The block can then be reread or rewritten. An attempt to rewrite the block destroys the contents of the remainder of the tape or track. See Using the BSP Macro to Backspace a Physical Record for information on using the BSP macro to process PDSEs.

The direction of movement is toward the load point or the beginning of the extent. You can not use the BSP macro if the track overflow option was specified or if the CNTRL, NOTE, or POINT macro is used. The BSP macro should be used only when other device control macros could not be used for backspacing.

Any attempt to backspace across the beginning of the data set on the current volume results in return code X'04' in register 15, and your tape or direct access volume is positioned before the first block. You cannot issue a successful backspace command after your EODAD routine is entered unless you first reposition the tape or direct access volume into your data set. CLOSE TYPE=T can position you at the end of your data set.

You can use the BSP macro to backspace VSE tapes containing embedded checkpoint records. If you use this means of backspacing, you must test for and bypass the embedded checkpoint records. You cannot use the BSP macro for VSE 7-track tapes written in translate mode.