This section is for the programmer who wants to create an address space. Perhaps the address space is for a subsystem that has "outgrown" the address space it shared with other programs; perhaps it will be for a set of programs that provide a service for programs in other address spaces. Perhaps the subsystem or the programs need to have more control over their environment.

One way for a program to create an address space, without involving an MVS™ operator, is by issuing a START command through the MGCR macro. The program must have a procedure in SYS1.PROCLIB, representing the first program that will execute in the created address space. The program can assign the dispatching priority for the programs that will run in the created address space. The initialization can include cross memory macros that establish a cross memory environment for the created address space.

An easier way to accomplish the same objectives is to issue the ASCRE macro. The ASCRE macro creates a address space that can start after the system is initialized and receive the services of all MVS components. It can set up cross memory linkages so that programs in the created address space can call programs in the creating program's address space. It can set a dispatching priority for the programs that run in the created address space and can specify that the address space exist after the task that represents the creating program terminates. (For simplicity, in this section the term "creating program" refers to the address space of the program that is issuing the ASCRE macro. The term "new address space" refers to the address space that the ASCRE macro creates.)

The system considers the new address space to be a system address space, and it will show up as such when the operator issues a DISPLAY A command, unless ATTR=JOBSPACE is specified on the ASCRES macro. Program properties table (PPT) values determine the attributes of the programs that execute in the new address space.