A single instruction in microcode. It is the most elementary instruction in the computer, such as moving the contents of a register to the arithmetic logic unit (ALU). It takes several microinstructions to carry out one complex machine instruction (CISC). Also called a "micro-op" or "µop," microinstructions differ within the same computer family and even the same vendor. For example, although all are x86 chips, the microcode for Intel's Pentium 4, Pentium M and AMD's Athlon are not the same. The software programmer never sees microinstructions, and they are not documented for the public. See
microcode.