Program counter - Definition and Overview

The program counter (also called the instruction pointer in some computers) is a register in a computer processor which indicates where the computer is in its instruction sequence. Depending on the details of the particular machine, it holds either the address of the instruction being executed, or the address of the next instruction to be executed. The program counter is automatically incremented for each instruction cycle so that instructions are normally retrieved sequentially from memory. Certain instructions, such as branches and subroutine calls, interrupt the sequence by placing a new value in the program counter.

In most processors, the instruction pointer is incremented immediately after fetching a program instruction; this means that the target address of a branch instruction is obtained by adding the branch instruction's operand to the address of the next instruction (byte or word, depending on the computer type) after the branch instruction.