Microcode is the name for a number of instructions or data structures which are involved in implementing higher-level machine language in many processors, especially microprogrammed ones. Microcode is on memory that is very fast to access. When a machine level instruction needs to be executed, microcode tells the processor what electronic circuits should be used. When a new processor is designed, an engineer also writes the microcode for the instructions of machine language. This is called Microprogramming, the resulting code is called a microprogram. 