21.3. The program status word
In a mainframe instruction stream, the next instruction is pointed to by the program status word (PSW). The current instruction is the only instruction according to the architecture. Everything else is considered to be data. Until the current instruction completes and the PSW changes its address, we can never be sure of what the next instruction is.
What is the program status word? The PSW in each CPU contains information required for the execution of the currently active program. In the z/Architecture, it is 128 bits long and includes the instruction address, condition code, and other control fields.
There are different ways that a PSW can get the address of the next instruction:
If this instruction is not a branch, ...
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