Deallocating Data Sets

When you connect data sets to a program in the foreground, the connection remains until you:

Log off TSO/E - All data sets allocated to your TSO/E session are deallocated when you log off.
Issue the FREE command - The FREE command releases specified data sets from previous allocations. For information about the FREE command, see Releasing Data Sets with the FREE Command.
Specify the REUSE operand with an ALLOCATE command - The REUSE operand frees and then reallocates a ddname to a specified data set. For information about the REUSE operand, see REUSE Operand.

To allow other data sets to connect to a ddname, you need to deallocate data sets when a program is finished with them. When you deallocate a data set, the system frees the connection to the ddname, and either deletes the data set or stores it, depending on what was specified when the data set was allocated.