Computer Basics - Machine Cycle and Instruction Execution

The machine cycle describes the sequence of steps a computer follows to process and execute instructions. Every task performed by a computer, from simple calculations to complex applications, is broken down into individual instructions that follow this cycle. Understanding the machine cycle helps explain how software commands are converted into hardware actions.

Instruction Fetch Phase

During the fetch phase, the control unit retrieves the next instruction from main memory. The address of this instruction is stored in a special register, and the instruction itself is transferred to the instruction register. This step ensures that the CPU knows exactly which operation needs to be performed next.

Instruction Decode Phase

In the decode phase, the control unit interprets the fetched instruction. It identifies the type of operation required, such as arithmetic, logical, or data movement, and determines which hardware components will be involved. This phase prepares the CPU to execute the instruction correctly by setting up necessary control signals.

Instruction Execute Phase

The execute phase is where the actual operation takes place. The arithmetic logic unit performs calculations or logical comparisons, memory may be accessed for data storage or retrieval, and results are generated. This phase transforms the instruction into a real action within the computer system.

Store and Repeat Process

After execution, the result may be stored in a register or written back to memory, depending on the instruction. The program counter is then updated to point to the next instruction. This continuous cycle of fetching, decoding, executing, and storing allows the computer to run programs smoothly and efficiently.