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Program counter
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<p>The program counter (PC), commonly called the instruction pointer (IP) in <a href="/facts/Intel/SMF0gJJX">Intel</a> <a href="/facts/X86/Kypq5fgu">x86</a> and <a href="/facts/Itanium/0wkjSDpe">Itanium</a> <a href="/facts/Microprocessor/Fx9CaQht">microprocessors</a>, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer, is a <a href="/facts/Processor_register/32RvbUdz">processor register</a> that indicates where a <a href="/facts/Computer/SQe1aK05">computer</a> is in its <a href="/facts/Computer_program/e38jH9N9">program</a> sequence. </p><p>Usually, the PC is incremented after fetching an <a href="/facts/Instruction_(computer_science)/8p8vwUeE">instruction</a>, and holds the <a href="/facts/Memory_address/7EsUmbea">memory address</a> of ("<a href="/facts/Pointer_(computer_programming)/fPoNzy9b">points</a> to") the next instruction that would be executed. </p><p>Processors usually fetch instructions sequentially from <a href="/facts/Computer_memory/hQKVQ51J">memory</a>, but <i>control transfer</i> instructions change the sequence by placing a new value in the PC. These include <a href="/facts/Branch_(computer_science)/obBGrnor">branches</a> (sometimes called jumps), <a href="/facts/Subroutine/9vFJrg0A">subroutine</a> calls, and <a href="/facts/Return_statement/lK7c71aa">returns</a>. A transfer that is conditional on the truth of some assertion lets the computer follow a different sequence under different conditions. </p><p>A branch provides that the next instruction is fetched from elsewhere in memory. A subroutine call not only branches but saves the preceding contents of the PC somewhere. A return retrieves the saved contents of the PC and places it back in the PC, resuming sequential execution with the instruction following the subroutine call. </p>