Dynamic allocation routines allocate, free, concatenate, and deconcatenate data sets dynamically, that is, during problem program execution. In the TSO/E environment, dynamic allocation permits the terminal monitor program, Command Processors, and other problem programs executing in the foreground region to allocate data sets after LOGON and free them before LOGOFF.

Programs that execute in the TSO/E environment can access dynamic allocation directly, using SVC 99, or through the dynamic allocation interface routine (DAIR). Though its use is not suggested because of reduced functions and additional system overhead, DAIR is documented in this book to provide compatibility for existing programs that use it. DAIR can be used to obtain information about a data set and, if necessary, invoke dynamic allocation routines to perform the requested function.

For a complete discussion of dynamic allocation, see z/OS MVS Programming: Authorized Assembler Services Guide.