 Sometimes users take advantage of the unintended or undocumented operation of hardware to serve some purpose, in which case a flaw may be considered a feature.This gives rise to the often ironically employed acronym INABIAF, "It's Not A Bug It's A Feature".For example, undocumented instructions, known as illegal opcodes, on the MOS Technology 6510 of the Commodore 64 and MOS Technology 6502 of the Apple II computers are sometimes utilized.