In either event, the system operators would often need to demount the devices, and a started task – DEALLOC – was often provided for this purpose.
Simply entering the command at the system console would run the started task, which consisted of just one step.
However, due to the design of Job Management, DEALLOC must actually exist in the system's procedure library, SYS1.PROCLIB, lest the start command fail.
As explained further in "Usage" below, the name "BR14" comes from the IBM assembler-language instruction "Branch (to the address in) Register 14", which by convention is used to "return from a subroutine".
Example JCL would be : To create a Partitioned Data Set: IEFBR14 consisted initially of a single instruction a "Branch to Register" 14.
BR 14 is identically equivalent to BCR 15,14 (Branch Always [ mask = 15 = always ] to the address contained in general purpose register 14).
Since IEFBR14 was always invoked by the functional equivalent of the canonical BALR 14,15 instruction, the return code in register 15 was always non-zero.
Initially, programmers were not using all properties of the Job Control Language, anyway, so an indeterminate return code was not a problem.