Microoperations

Microoperations are the elementary operations performed by a computer’s datapath on data stored in registers and internal buffers. They represent the smallest units of work a processor can perform during a single clock cycle and are the building blocks used to implement machine instructions within a CPU’s microarchitecture.

Typical microoperations fall into several categories. Register transfer microoperations move data from one register to another or to special registers (for example, R1 <- R2, or R3 <- R1). Arithmetic and logic microoperations perform computations on register contents (ADD, SUB, AND, OR, NOT, INC, DEC) and place the result in a register. Shift and rotate microoperations move or rotate register contents (SHL, SHR, ROL, ROR). Memory-related microoperations move data between memory and the register file and may update address or data registers. Some microoperations also update condition or status flags, which influence subsequent control decisions. Conditional microoperations execute only when certain status conditions are met, enabling branches and other control flow.

Microoperations are coordinated by the CPU’s control unit. In microprogrammed control, a microinstruction encodes a set of control signals that trigger a sequence of microoperations, effectively implementing an instruction as a short program of microinstructions. In hardwired control, dedicated combinational and sequential logic generates the necessary control signals directly from the instruction fields and current state.

Together with the datapath, microoperations define how a machine instruction is realized at the hardware level. They are central to discussions of computer architecture and microarchitecture and to the design of efficient processors.