Computer Systems - Notes

Introduction to Computer System

A computer is an electronic device that:

• Accepts data (input).

• Processes the data.

Generates a result (output).

• A computer system includes:

  • A computer.

  • Additional hardware.

  • Software.

• Components of a computer system:

  • Central Processing Unit (CPU).

  • Memory.

  • Input/Output devices.

  • Storage devices.

Central Processing Unit (CPU)

• The electronic circuitry that carries out actual processing.

• Often referred to as the "brain" of the computer.

• Also known as a processor.

• Can be placed on one or more microchips called integrated circuits (ICs).

• ICs are made of semiconductor materials.

• Composed of:

  • Arithmetic Logic Unit (ALU): Performs arithmetic and logic operations.

  • Control Unit (CU): Controls instruction execution, interprets instructions, and manages data flow.

Input Devices

• Devices that send control signals to a computer.

• Convert input data into a digital form that the computer can accept.

• Examples:

  • Keyboard.

  • Mouse.

  • Scanner.

  • Touch screen.

• Braille keyboards are available for visually impaired users.

• Voice input (e.g., Google voice search) is also a method of input.

• Input data is temporarily stored in the main memory (RAM).

Output Devices

• Devices that receive data from a computer system for:

  • Display.

  • Physical production.

• Convert digital information into human-understandable form.

• Examples:

  • Monitor.

  • Projector.

  • Headphone.

  • Speaker.

  • Printer.

• Braille display monitors are available for visually challenged users.

• Common types of printers:

  • Inkjet.

  • Laserjet.

  • Dot matrix.

  • 3D-printer: Builds physical replicas of digital 3D designs, used in manufacturing and medical fields.

Evolution of Computer

• Computing devices have evolved from simple calculators to powerful data processors.

• Key inventions in computing technology:

  • Abacus:

    • Invented around 500 BC.

    • A mechanical device for simple arithmetic calculations.

  • Pascaline:

    • Invented in 1642 by Blaise Pascal.

    • A mechanical calculator that could perform addition and subtraction directly, and multiplication and division through repeated addition and subtraction.

  • Analytical Engine:

    • Invented in 1834 by Charles Babbage.

    • A mechanical computing device for inputting, processing, storing, and displaying output.

    • Considered the basis of modern computers.

  • Tabulating Machine:

    • Designed in 1890 by Herman Hollerith.

    • Summarized data stored on punched cards.

    • A step towards programming.

  • Turing Machine:

    • Invented in 1937.

    • A general-purpose programmable machine capable of solving any problem by executing programs stored on punched cards.

  • EDVAC/ENIAC:

    • Invented in 1945 based on the concept introduced by John Von Neumann.

    • Stored program computer that could store both data and programs in memory.

  • Transistor:

    • Invented in 1947 at Bell Labs.

    • Replaced vacuum tubes using semiconductor materials.

  • Integrated Circuit (IC):

    • Invented in 1970.

    • A silicon chip containing an entire electronic circuit on a small area.

    • Reduced the size of computers drastically.

Von Neumann Architecture

• Consists of:

  • CPU for processing arithmetic and logical instructions.

  • Memory to store data and programs.

  • Input and output devices.

  • Communication channels.

• Electronic Numerical Integrator and Computer (ENIAC) is the first binary programmable computer based on Von Neumann architecture.

Technological Advancements

• Large Scale Integration (LSI):

  • Allowed integration of the complete CPU on a single chip, called a microprocessor.

• Moore’s Law:

  • Predicted exponential growth in the number of transistors that could be assembled on a single microchip.

• Very Large Scale Integration (VLSI):

  • Integrated around 3 million components on a small-sized chip in the 1980s.

• Super Large Scale Integration (SLSI):

  • Fabrication of high-density transistors and other components (approximately $10^6$ components) on a single IC.

• IBM introduced its first personal computer (PC) for the home user in 1981, and Apple introduced Macintosh machines in 1984.

• Graphical User Interface (GUI) based operating systems increased PC popularity.

• Growth of the World Wide Web (WWW) in the 1990s accelerated computer usage.

• Laptops made personal computing portable.

• Smartphones, tablets, and other personal digital assistants leveraged advancements in processor miniaturization, faster memory, and high-speed data and connectivity mechanisms.

• The next wave of computing devices includes wearable gadgets (smart watches, lenses, etc.) and smart appliances as part of the Internet of Things (IoT), using Artificial Intelligence (AI).

Moore's Law

• Introduced in 1965 by Intel co-founder Gordon Moore.

• Predicted that the number of transistors on a chip would double every two years, while costs would be halved.

Computer Memory

• Computer systems need memory to store data and instructions for processing.

• Types of memory:

  • Primary memory (main memory).

  • Secondary memory (storage device): Used for permanent storage of data, instructions, and results.

Units of Memory

• A computer system uses binary numbers to store and process data.

• Bit: The basic unit of memory, represented by the binary digits 0 and 1.

• Nibble: A 4-bit word (e.g., 1001, 1010, 0010).

• Byte: An 8-bit word or two nibbles (e.g., 01000110, 01111100, 10000001).

Types of Memory

• Primary Memory:

  • Essential for a computer system.

  • Programs and data are loaded into primary memory before processing.

  • The CPU interacts directly with primary memory to perform read or write operations.

  • Types:

    • Random Access Memory (RAM):

    • Volatile: Retains data as long as power is supplied.

    • Used to store data temporarily while the computer is working.

    • Referred to as main memory.

    • Faster than secondary memory.

    • Read Only Memory (ROM):

    • Non-volatile: Contents are not lost when power is turned off.

    • Used for small but faster permanent storage for contents that are rarely changed.

    • Example: Startup program (boot loader) that loads the operating system.

• Cache Memory:

  • Faster than RAM but not as fast as a computer processor.

Measurement units for digital data