Programszámláló

Programszámláló (Hungarian for “program counter”) is a special register in a computer's central processing unit that holds the address of the next instruction to be fetched from memory. It is also known as the instruction pointer or program counter in English. The program counter is automatically incremented after each instruction fetch, except when a control transfer instruction such as a jump, branch, or call modifies its value, allowing the CPU to alter the sequential flow of execution.

The concept of a program counter dates back to early computer designs, where it was essential for supporting unstructured instruction sequencing. In modern microprocessors, the PC is usually part of the control unit and is closely coupled with the instruction decode and execute stages. Some architectures support multiple program counters, such as for pipelining or multiprocessing, and some allow user-level manipulation of the PC for emulator or debugging purposes.

Program counters are fundamental to the fetch–decode–execute cycle and are integral to features like interrupts, exceptions, and context switching. Their reliability and accuracy are critical for system stability, and hardware typically includes mechanisms to protect the PC from corruption by providing error‑detecting and recovery logic.