Editing P-code machine (section)

===Environment===
Similar to a real target CPU, the P-System has only one stack shared by procedure stack frames (providing [[Return statement|return address]], etc.) and the arguments to local instructions. Three of the machine's [[Processor register|registers]] point into the stack (which grows upwards):
* SP points to the top of the stack (the [[stack pointer]]).
* MP marks the beginning of the active stack frame (the [[mark pointer]]).
* EP points to the highest stack location used in the current procedure (the [[extreme pointer]]).

Also present is a constant area, and, below that, the [[Dynamic memory allocation|heap]] growing down towards the stack. The NP (the [[new pointer]]) register points to the top (lowest used address) of the heap. When EP gets greater than NP, the machine's memory is exhausted.

The fifth register, PC, points at the current instruction in the code area.