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1. Fetch-Decode-Execute Cycle
An easy explanation of how the CPU
processes instructions

2. What is the Fetch-Decode-Execute
Cycle?
• The CPU follows the Fetch-Decode-Execute
cycle to process instructions:
• 1. **Fetch**: Retrieves the next instruction
from memory.
• 2. **Decode**: Interprets what the
instruction means.
• 3. **Execute**: Carries out the instruction.

3. Step 1: Fetch
• • The Program Counter (PC) holds the
memory address of the next instruction.
• • This address is copied to the Memory
Address Register (MAR).
• • The instruction is fetched from memory and
stored in the Memory Data Register (MDR).
• • The instruction is copied to the Current
Instruction Register (CIR).
• • The Program Counter (PC) is incremented by
1.

4. Step 2: Decode
• • The instruction in the CIR is analyzed.
• • The CPU's Control Unit determines what the
instruction means.
• • The necessary operations are prepared for
execution.

5. Step 3: Execute
• • The CPU sends control signals to relevant
components.
• • The instruction is carried out (e.g.,
calculations, data movement, etc.).
• • The cycle repeats for the next instruction.

6. Summary
• • The Fetch-Decode-Execute cycle is how the
CPU processes instructions.
• • **Fetch**: Gets the next instruction.
• • **Decode**: Understands what to do.
• • **Execute**: Carries out the task.
• This cycle happens millions of times per
second!