Users issue the TSO/E ALLOCATE command to create new data sets, allocate data sets to a job, and create system output (SYSOUT) data sets. You do not have to perform any tasks to make the ALLOCATE command available to users. You can, however, customize how users allocate data sets.

You can use Storage Management Subsystem (SMS) to manage your system's data and storage and simplify data set allocation for your users. With SMS, you define classes such as data class, management class, and storage class that contain particular allocation, management, and storage attributes for data sets. You define the classes using automatic class selection (ACS) routines. For information about the classes and ACS routines, see .

When users allocate a data set, they do not have to specify different operands for particular data set attributes. Instead, they can specify the DATACLASS, MGMTCLAS, and STORCLAS operands on the ALLOCATE command, which simplify data set allocation. For more information about the ALLOCATE command and its operands, see .

You can use SYS1.PARMLIB member IKJTSOxx to set a default value for the data set disposition specified on the ALLOCATE command. For more information, see Specifying a default data set disposition for the ALLOCATE command.

You can use the MVS™ allocation input validation routine (exit IEFDB401) to change the information users specify on the ALLOCATE command. If you use Program Control Facility (PCF), you must not use the MVS allocation input validation routine. PCF uses the routine to control allocation. For more information about the MVS allocation input validation routine, see .

When users issue the ALLOCATE command to allocate SYSOUT data sets, they specify operands related to the printer and printing options they want. You can use OUTPUT JCL statements to define output descriptors that associate different printers and options with a single name, the name of the output descriptor. If you have JES2 installed, you and your installation's users can also use the TSO/E OUTDES command to define output descriptors. When users issue the ALLOCATE command, they can specify the OUTDES operand with the name of the output descriptor. They do not need to specify the individual printing options. For more information about using OUTPUT JCL statements to define output descriptors, see Defining OUTPUT JCL statements. For more information about the OUTDES command, see .

Users can also use the space management service to manage the free space in data sets. Space management can compress, reallocate, or create a data set. Space management uses default allocation and protection data set attributes, but you can change the default values for your own requirements. Changing the defaults for managing data set space describes the values you can change.

TSO/E provides initialization and termination exits that you can use to customize the ALLOCATE command. The initialization exit receives control before the ALLOCATE command processor invokes the parse service routine, and can change operands supplied by the user or pass the address of a new command buffer. The termination exit receives control just before the ALLOCATE command terminates processing, and can perform clean-up processing, such as releasing storage obtained by the initialization exit. For more information about the ALLOCATE exits, see Writing exits for the ALLOCATE command.