Fetch-execute cycle
The fetch-execute cycle (sometimes expanded and known as the Fetch-decode-execute cycle or FDX) is the sequence of actions that a central processing unit performs to execute each machine code instruction in a program. At the beginning of each cycle the Central processing unit (CPU) presents the value of the program counter on the address bus. The CPU then fetches the instruction from main memory via the data bus into the instruction register. From the instruction register, the data forming the instruction is decoded and passed to the control unit which sends a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers, passing them to the Arithmetic logic unit (ALU) to add them together and writing the result back to a register. The program counter is then incremented to address the next instruction and the cycle is repeated. The fetch-execute cycle was first proposed by John von Neumann.
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