To allow the AVR option to process nonstandard magnetic tape labels, you must write a routine to supply AVR with information about them. Insert it into the control program replacing the IBM-supplied routine that causes AVR to reject tape volumes with non-standard labels. Your routine returns information to AVR that consists of a validity indication and the location within the nonstandard label of the volume serial number field.

OPEN, EOV, and CLOSE will always turn the DEB31UCB on in the work area to signify that DXDEBUCB is a 31-bit UCB address. Although the UCB address field will be four bytes, it typically will contain a three-byte address. The modeset byte is moved from the DEBSDVM field to the DEBSDVMX field to enable 31 bit UCB addresses to be accommodated.