The execute direct access program (XDAP) is a macro instruction used to read, verify, or update a block on a direct access volume. This information covers the XDAP macro instruction, including information for compatibility with other IBM® operating systems, what the XDAP macro does, and how to use it. It also discusses the macro instructions used with XDAP and the control blocks that are generated. However, IBM suggests using an access method such as VSAM in place of XDAP.

Because most of the specifications for XDAP are similar to those for the execute channel program (EXCP) macro instruction, you should be familiar with the information in IDAW Requirements for EXCP Requests of this publication. You should also be familiar with the information in z/OS DFSMS Using Data Setsz/OS DFSMS Using Data Sets that provides how-to information for using the access method routines of the system control program.

If you are not using the standard IBM data access methods, by issuing XDAP you can generate the control information and channel program necessary for reading or updating the records of a data set.

While XDAP cannot be used to add blocks to a data set, it can be used to change the keys of existing blocks. Any block configuration and any data set organization can be read or updated.

XDAP requires less storage than do the standard access methods. However, XDAP does not provide many of the control program services that are included in the access methods. For example, when XDAP is issued, the system does not block or unblock records and does not verify block length.

All virtual addresses that you use with XDAP except the OPEN and CLOSE parameter lists, DCBE, and IOBE must be 24–bit.