After the system is initialized and the job entry subsystem is active, jobs may be submitted for processing. When a job is activated through START (for batch jobs), LOGON (for time-sharing jobs) or MOUNT, a new address space must be allocated. Note that before LOGON, the operator must have started TCAM or VTAM/TCAS, which have their own address spaces. Figure 1 is a virtual storage map containing or naming the basic system component address spaces, the optional TCAM and VTAM® system address spaces, and a user address space.

The system resources manager decides, based on resource availability, whether a new address space can be created. If not, the new address space will not be created until the system resources manager finds conditions suitable.