Microcommand

Microcommand refers to a fundamental, elementary operation within a computer's central processing unit (CPU). These are the simplest instructions that a CPU can execute, forming the building blocks for more complex operations. When a CPU fetches and decodes an instruction from memory, it breaks that instruction down into a sequence of microcommands. Each microcommand manipulates the CPU's internal registers, arithmetic logic unit (ALU), or control signals.

The sequence of microcommands required to execute a single machine instruction is stored in a special memory called the control store or microprogram memory. This microprogram dictates the step-by-step process for each machine instruction. For example, a simple addition instruction might be translated into a series of microcommands that fetch operands from registers, send them to the ALU for addition, and then store the result back into a register.

The concept of microprogramming was developed to simplify the design of complex instruction sets. Instead of building dedicated hardware for every possible machine instruction, designers can implement them using sequences of microcommands, making the CPU's control logic more flexible and easier to modify. Modern CPUs often use a hybrid approach, with some instructions executed directly by hardware (hardwired control) and others by microprograms. The term "micro-operation" is often used interchangeably with microcommand.