A group of (usually) bistable devices that are used to store information within a computer system for high-speed access. A register of n bistables can store a word of length n bits, which can represent any n bits of information. Different interpretations can be given to the bit configuration stored in the register; for example, the configuration could represent an instruction, a binary number, an alphanumeric character, etc. A register is often the same size as the computer word; it may also be byte- or character-size or some other size as required. Some registers can behave as counters as well, or they may behave as shift registers. See also memory hierarchy.