Program counter

The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer,is a processor register that indicates where a computer is in its program sequence. The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer,is a processor register that indicates where a computer is in its program sequence. In most processors, the PC is incremented after fetching an instruction, and holds the memory address of ('points to') the next instruction that would be executed. (In a processor where the incrementation precedes the fetch, the PC points to the current instruction being executed.) Processors usually fetch instructions sequentially from memory, but control transfer instructions change the sequence by placing a new value in the PC. These include branches (sometimes called jumps), subroutine calls, and returns. A transfer that is conditional on the truth of some assertion lets the computer follow a different sequence under different conditions.