Overview of Von Neumann Architecture

Sep 26, 2024

Lecture on Von Neumann Architecture

Introduction

  • Final video in a series of three discussing computer systems.
  • Focus on Von Neumann architecture, fundamental to modern computers.
  • Prior computing machines had fixed programs (e.g., desktop calculators).
  • Stored program concept introduced by John von Neumann in 1945.

Von Neumann Architecture

  • Key Characteristics:
    • Central Processing Unit (CPU): Contains a Control Unit and Arithmetic Logic Unit (ALU).
    • Onboard cache: Small, high-speed memory for instruction/data management.
    • Internal clock: Synchronizes CPU components.
  • Functionality:
    • Fetches, decodes, and executes instructions stored in main memory.
    • Not the most efficient design but simple and foundational.

Memory and Instruction Cycle

  • Instructions stored in main memory with specific addresses.
  • Processor fetches instructions to registers for execution.
  • Registers:
    • Program Counter (PC): Holds the address of the next instruction.
    • Memory Address Register (MAR): Address of data to fetch/store.
    • Memory Data Register (MDR): Holds data fetched from/to be written to memory.
    • Accumulator: Stores results of ALU calculations.

Fetch-Execute Cycle

  • Fetch:
    • PC checked -> Address in MAR -> Instruction fetched to MDR.
    • PC incremented for the next instruction.
  • Decode:
    • Instruction loaded into CPU cache for quick access.
    • Control Unit decodes the instruction.
  • Execute:
    • Depends on instruction (e.g., fetch data, perform arithmetic, write back to memory).

Example Execution

  • Program performs a series of fetch-execute cycles:
    1. First Cycle:
      • Fetch instruction from address 1, decode, and execute (load value into accumulator).
    2. Second Cycle:
      • Fetch instruction to add value from address 6, decode, add to accumulator.
    3. Third Cycle:
      • Store accumulator value back to memory at address 6.
    4. Fourth Cycle:
      • Fetch end program instruction and terminate.

Summary

  • Von Neumann architecture integrates control unit, ALU, memory unit, inputs, and outputs.
  • Based on stored program concept where instructions and data share memory.
  • Registers and cycles crucial for instruction processing.
  • Example demonstrated a simple arithmetic operation.