Machine Cycle

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 Machine Cycle – The CPU’s Step-by-Step Process

The machine cycle (also called the instruction cycle) is the process the CPU follows to execute an instruction. It consists of four main stages:

Stages of the Machine Cycle

  • Fetch – The CPU will be retrieves the instructions from memory.
  • Decode – The CPU interprets the instruction.
  • Execute – The CPU performs the instruction.
  • Store – The CPU saves the result in memory or a register.

Each cycle is controlled by the Control Unit (CU) and processed through the Arithmetic & Logic Unit (ALU) when necessary.

Detailed Breakdown of Each Stage

1. Fetch (Getting the Instruction)

  • The Program Counter (PC) holds all the addresses of the next instruction.
  • The Control Unit (CU) sends a signal to fetch the instruction from memory (RAM).
  • The instruction is placed into the Instruction Register (IR).

2. Decode (Understanding the Instruction)

  • The Control Unit deciphers the instruction.
  • It determines what actions are required (e.g., arithmetic, logic, memory access).
  • If needed, it prepares the ALU for calculations.

3. Execute (Performing the Instruction)

  • The CPU carries out the instruction using the ALU (for calculations) or registers.
  • Logical decisions (such as comparisons) are processed.
  • The result is generated.

4. Store (Saving the Result)

  • The result is stored in a register or memory for future use.
  • The Program Counter (PC) is to be updated to point to the next instruction.
  • The cycle repeats for the next operation.

Machine Cycle and CPU Speed

  • The number of the cycles are per second is measured in Hertz (Hz).
  • A 1 GHz processor can perform 1 billion machine cycles per second.
  • More cores and higher clock speeds improve efficiency.

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