(2348) IGCSE Computer Science 2023-25 ​​- Topic 3: HARDWARE (1) - COMPUTER ARCHITECTURE - Von Neumann & CPU

Overview of Hardware

  • Hardware is the physical components of a computer system.

  • Types of hardware include:

    • Input Devices: Keyboard, mouse, barcode readers.

    • Output Devices: Monitors, printers, speakers.

    • Internal Components: CPU, memory, storage.

    • External Storage: USB drives, external hard drives.

Central Processing Unit (CPU)

  • Definition: The CPU, or microprocessor, is central to all modern computer systems.

  • Function: Executes and processes all instructions and controls communication among components.

    • Integrated Circuit: The CPU is typically an integrated circuit on a single microchip.

History of CPU and Von Neumann Architecture

  • Historical Context: Early computers required human interaction for data input.

  • John Von Neumann: Developed the concept of the stored-program computer in the mid-1940s.

    • Importance: The Von Neumann architecture is the foundation for contemporary computer designs.

    • Key Features:

      • Central Processing Unit (CPU) can access memory directly.

      • Memory can store both programs and data.

      • Programs executed sequentially.

Components Inside the CPU

  • The CPU consists of three main components:

    1. Control Unit (CU):

      • Reads instructions from memory.

      • Uses the Program Counter (PC) register to track instruction locations.

      • Manages data flow and ensures synchronization within the computer.

    2. Arithmetic Logic Unit (ALU):

      • Performs mathematical calculations and logical operations.

      • Can have multiple ALUs for simultaneous operations.

      • Handles addition, subtraction, AND/OR logic, and more.

    3. Registers:

      • Memory Address Register (MAR): Stores addresses of data in memory.

      • Memory Data Register (MDR): Holds data being transferred to/from memory.

      • Other registers include the Current Instruction Register (CIR) and Accumulator (ACC).

System Clock and Performance

  • Clock Speed: Controls synchronization among components.

    • Measured in hertz (Hz); higher frequency means faster processing.

  • Comparison of clock speeds:

    • 1980s: 3-5 MHz (3-5 million cycles/second)

    • Present: 3-5 GHz (3-5 billion cycles/second)

Data Handling in CPU

  • Data Transfer Process:

    • The CPU retrieves program data from the hard disk into RAM.

    • RAM enables faster access for operational data versus hard disk.

Buses in CPU Communication

  • Types of Buses:

    1. Data Bus: Transfers actual data between components.

    2. Address Bus: Carries memory addresses from CPU to memory or I/O devices.

    3. Control Bus: Carries control signals and clock pulses.

Memory and Data Retrieval

  • Memory Structure: Memory is organized by addresses and contents.

    • Each memory location has a unique address with stored binary values.

Reading and Writing Operations

  • Read Operation Process:

    1. MAR stores the address to read.

    2. The read signal retrieves the data into the MDR.

  • Write Operation Process:

    1. Data is placed into the MDR.

    2. MAR stores the address where the data should be written.

    3. Write signal stores the data in memory.

Summary and Next Steps

  • The next lesson will cover the fetch-decode-execute cycle, completing the topic of computer architecture.