Explicit and Implicit Allocation

In a TSO/E session, you can have explicit or implicit allocation.

Explicit allocation is a direct request for a data set, which can occur from:
- Job control language (JCL) - JCL defines a data set as a resource for a job through a data definition (DD) statement. For example, your TSO/E terminal session is a job defined by your LOGON procedure. The LOGON procedure contains JCL DD statements for the data sets that create your TSO/E environment.
  For more information about JCL, see z/OS MVS JCL Reference.
- The ALLOCATE command - You can issue the ALLOCATE command in the foreground from a terminal or from a CLIST. You use the ALLOCATE command to connect a data set to a program for input or output.
- The ALLOCATE function of the UTILITIES option of ISPF/PDF - You can use it to define a new data set that you can later edit. You cannot, however, use ISPF/PDF to connect a data set to a program.
Implicit allocation is allocation that occurs indirectly as a result of a command other than the ALLOCATE command. For example, when you issue the EDIT command or select the ISPF/PDF EDIT option, the data set you specify and other data sets needed for the editing process are allocated implicitly. You can then display and edit the data set you specified.

This chapter covers explicit allocation using the: