Sixth and lastly, the HLT instruction is very special, since it causes the computer to cease going through its fetch/decode/execute cycle. When HLT is executed, a special bit is set and the cycle of operands is no longer done. Some computers have external buttons that when pressed cause the computer to halt, resume where they left off, or start from 0. Most computers, when they come to life after the power is termed on, start executing a system program that is stored at 0. Thus, 0 is loaded into the PC register and the fetch/decode/execute cycle is begun. This is called booting the computer because it seems as though the computer is pulling itself up by its own bootstraps, or starting itself in a seemingly impossibly circular fashion.