Determining Version, Release, and Modification Level of DFSMS

The first byte of DFARELS contains a binary value that indicates the level of DFSMS on which your program is running:

Value: Meaning
0: Your program is not executing on DFSMS; it is executing on MVS/XA DFP Version 2 or MVS/DFP Version 3 and the following three bytes also contain zeroes. On those two products you can determine the release level by examining the two-byte field DFAREL. DFAREL is described in the comments in IHADFA.
1: Your program is running on DFSMS/MVS and the following three bytes designate the version, release and modification level of DFSMS/MVS. A value of X'01010200' in DFARELS designates DFSMS/MVS Version 1, Release 2, Modification level 0.
2: Your program is running on the level of DFSMS that is exclusive to OS/390® or one of the first two releases of z/OS®. A value of X'02020A00' in DFARELS designates DFSMS for OS/390 Version 2 Release 10, Modification level 0. DFSMS was not modified in the first two releases of z/OS, so these releases also have a value of X'02020A00'.
>3: Your program is running on a level of DFSMS that is part of a hypothetical replacement product after all versions and releases of z/OS. The system never returns this value. This represents IBM's intent in case there is such a product. The following three bytes designate the version, release, and modification level of that product. The value in the other three bytes is X'010100' or higher. It may differ from the level of installed z/OS.
3: Your program is running on a level of DFSMS that is exclusive to z/OS Version 1 Release 3 or higher. The following three bytes designate the version, release, and modification level of z/OS for which that DFSMS was designed. The value in the other three bytes is X'010300' or higher. It may differ from the level of installed z/OS.

IBM® intends that for any future level of the DFA, the 4-byte DFARELS will not contain a value smaller than any previous value. If your purpose in testing DFARELS is to determine whether a particular feature of DFSMS is available, then we suggest that your program test all four bytes of DFARELS. IBM intends that if one of the low-order three bytes of DFARELS contains a value that is smaller than the corresponding byte in the prior release, then a higher order byte will contain a larger value.

For compatibility with programs that were designed to run on MVS/XA DFP Version 2 or MVS/DFP Version 3, DFSMS sets DFAREL to the value X'3321', which designates MVS/DFP Version 3, Release 3, modification level 2. The last digit indicates that the system actually is at a higher level than DFP 3.3.2.

See also Call for DFSMS Level Determination for an alternative method of determining the level of DFSMS.

See Data Facilities Area (DFA) Fields for a layout of the fields of the Data Facilities Area (DFA) control block.