Editing Central processing unit (section)

===Fetch===
Fetch involves retrieving an [[instruction (computing)|instruction]] (which is represented by a number or sequence of numbers) from program memory. The instruction's location (address) in program memory is determined by the [[program counter]] (PC; called the "instruction pointer" in [[x86|Intel x86 microprocessors]]), which stores a number that identifies the address of the next instruction to be fetched. After an instruction is fetched, the PC is incremented by the length of the instruction so that it will contain the address of the next instruction in the sequence.{{Efn|Since the program counter counts ''memory addresses'' and not ''instructions'', it is incremented by the number of memory units that the instruction word contains. In the case of simple fixed-length instruction word ISAs, this is always the same number. For example, a fixed-length 32-bit instruction word ISA that uses 8-bit memory words would always increment the PC by four (except in the case of jumps). ISAs that use variable-length instruction words increment the PC by the number of memory words corresponding to the last instruction's length.}} Often, the instruction to be fetched must be retrieved from relatively slow memory, causing the CPU to stall while waiting for the instruction to be returned. This issue is largely addressed in modern processors by caches and pipeline architectures (see below).