For authorized application programs, VTAM® optionally gives control to asynchronous exit routines in supervisor state. The exit routines are branch entered from VTAM instead of being entered through the SYNCH macroinstruction. This allows for more efficient operation than if the exit routines were entered normally. The routines are entered in the storage protection key of the authorized program. This type of entry is provided only if SRBEXIT=YES is specified on the APPL definition statement. See Assigning operating system authorization for the definition of an authorized VTAM application program.