The allocation of the stack for each thread, including the initial processing thread (IPT), is part of a storage request to the system when the thread is first created. Other storage, not part of the stack, is also acquired at this time. These storage allocations are not shown in the storage report. The size of the stack portion of this storage is the stack maximum size plus a one megabyte (1M) guard area. After allocation, the guard area follows the stack initial size and runs through the end of the stack maximum size plus the 1M guard area. Increments to the stack for each thread do not result in additional storage requests to the system. They result in the movement of the beginning of the guard area no further than the maximum size of the stack. The stack initial, increment, and maximum sizes are controlled through the STACK64 and THREADSTACK64 runtime options.