Unit 1: Introduction to Digital Computers
1.1 Computer Definition & Characteristics
Computer Definition
A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data. It takes raw data as input, processes it according to a set of instructions (a program), and produces a result (output).
Characteristics of Computers
- Speed: Computers can perform billions of calculations per second. Their speed is measured in Megahertz (MHz) or Gigahertz (GHz).
- Accuracy: Computers are highly accurate. Errors, if any, are usually due to human error (incorrect data or instructions), not technological flaws. This is often referred to as GIGO (Garbage In, Garbage Out).
- Diligence: Unlike humans, a computer is free from monotony, tiredness, and lack of concentration. It can work continuously for hours without creating any errors.
- Versatility: Computers are multi-purpose. They can perform a wide variety of tasks, from simple calculations to complex simulations, entertainment, and communication.
- Storage Capacity: Computers can store vast amounts of data and retrieve it almost instantaneously. The storage capacity is growing exponentially with advancements in technology.
- Automation: Once a program is loaded into the computer's memory, the computer can execute it automatically without human intervention until the task is complete.
- Reliability: Modern computers are very reliable. They have a long life and their components rarely break down.
1.2 Evolution of Computers & Applications
Evolution of Computers (Generations)
- First Generation (1940s-1950s): Used vacuum tubes for circuitry. They were massive, expensive, and generated a lot of heat. Programming was done in machine language. Examples: ENIAC, UNIVAC.
- Second Generation (1950s-1960s): Replaced vacuum tubes with transistors, making computers smaller, faster, cheaper, and more reliable. Assembly language and early high-level languages like FORTRAN and COBOL were introduced.
- Third Generation (1960s-1970s): Characterized by the use of Integrated Circuits (ICs). This allowed for even smaller computers with keyboards and monitors. Operating systems were developed. Examples: IBM-360 series.
- Fourth Generation (1970s-Present): Based on microprocessors, which packed thousands of ICs onto a single silicon chip. This led to the development of personal computers (PCs). GUIs, mice, and handheld devices emerged.
- Fifth Generation (Present and Beyond): Focuses on Artificial Intelligence (AI), parallel processing, and quantum computing. Aims to develop devices that can respond to natural language and are capable of learning and self-organization.
Applications of Computers
- Business: For accounting, inventory management, marketing, etc.
- Education: Online classes, research, digital libraries.
- Healthcare: Patient records, medical imaging, diagnostics.
- Science and Engineering: Research, simulations, design (CAD).
- Entertainment: Gaming, movies, music.
- Government: E-governance, defense, data management.
- Communication: Email, social media, video conferencing.
1.3 Types of Computers
Computers can be classified based on their size, power, and purpose.
- Supercomputers: The fastest and most expensive computers. Used for highly complex tasks like weather forecasting, scientific simulations, and nuclear research.
- Mainframe Computers: Large, powerful computers used by large organizations (like banks and airlines) for critical applications and bulk data processing.
- Minicomputers (Mid-range computers): Multi-user computers that are less powerful than mainframes but more powerful than personal computers. Often used as network servers.
- Microcomputers (Personal Computers - PC): Small, relatively inexpensive computers designed for individual use. Includes desktops, laptops, tablets, and smartphones.
- Embedded Computers: Special-purpose computers that are part of a larger device or system. Found in cars, microwaves, and industrial machines.
1.4 Basic Organization of a Digital Computer
The basic organization of a computer system is based on the Von Neumann architecture. It consists of five major components.
Exam Tip: Always draw the Von Neumann Architecture diagram when asked about the basic organization of a computer. It clearly shows the relationship between the CPU, Memory, and I/O units.
- Input Unit: Takes data and instructions from the user. (e.g., Keyboard, Mouse)
- Central Processing Unit (CPU): The "brain" of the computer. It processes the data. It has two main sub-units:
- Control Unit (CU): Directs and coordinates most of the operations in the computer.
- Arithmetic Logic Unit (ALU): Performs arithmetic operations (+, -, *, /) and logical operations (AND, OR, NOT).
- Memory Unit: Stores data, instructions, and intermediate results. (e.g., RAM, ROM)
- Output Unit: Presents the processed data (information) to the user. (e.g., Monitor, Printer)
- Storage Unit: Stores data and programs permanently for future use. (e.g., Hard Disk, SSD)
1.5 Computer Design vs. Computer Architecture
Computer Architecture
Refers to the attributes of a system visible to a programmer. It's the what. It includes the instruction set, number of bits used for data, I/O mechanisms, and addressing techniques. Example: The specification that a processor will have a multiplication instruction.
Computer Organization
Refers to the operational units and their interconnections that realize the architectural specifications. It's the how. It includes details like control signals, interfaces between the computer and peripherals, and the memory technology used. Example: How the multiplication instruction is implemented (e.g., using a dedicated hardware unit or repeated addition).
Analogy: Think of designing a car. Architecture is deciding it will have four wheels, an engine, and seats for five people. Organization is deciding the specific type of engine, the material for the seats, and how the steering wheel connects to the wheels.
1.6 Hardware and Software
Hardware
The physical components of a computer system that you can touch and see. Examples: CPU, monitor, keyboard, motherboard, RAM.
Software
A set of instructions or programs that tells the hardware what to do. You cannot touch software.
- System Software: Manages and controls the computer hardware. It provides a platform for application software to run.
- Operating System (OS): The most important system software. (e.g., Windows, macOS, Linux)
- Utility Software: Performs maintenance tasks. (e.g., Antivirus software, disk cleanup tools)
- Application Software: Designed to perform specific tasks for the user. (e.g., Microsoft Word, Google Chrome, Photoshop)
1.7 Central Processing Unit (CPU)
As mentioned, the CPU is the primary component that executes instructions. It consists of:
- Arithmetic Logic Unit (ALU): The part of the CPU that handles all the calculations the CPU may need.
- Control Unit (CU): Extracts instructions from memory, decodes them, and executes them, calling on the ALU when necessary.
- Registers: Small, high-speed storage locations within the CPU used to temporarily hold data and instructions during processing. Important registers include the Program Counter (PC), Instruction Register (IR), and Accumulator.
1.8 Input and Output Devices
Input Devices
Hardware used to provide data and control signals to a computer.
- Keyboard: For typing text and numbers.
- Mouse: A pointing device.
- Scanner: Converts printed documents into digital format.
- Microphone: Captures audio.
- Webcam: Captures video.
Output Devices
Hardware used to communicate the results of data processing carried out by a computer.
- Monitor: Displays visual output.
- Printer: Produces a hard copy of documents.
- Speakers: Produce audio output.
- Projector: Displays output on a large screen.
1.9 Computer Memory & Storage
Memory is used to store data and instructions. It is organized in a hierarchy.
Primary Memory (Main Memory)
Volatile memory that holds data and instructions that the CPU is currently working with. It is directly accessible by the CPU.
- Random Access Memory (RAM): Volatile memory. Data is lost when power is turned off. This is the computer's "working memory".
- Read-Only Memory (ROM): Non-volatile memory. Data is not lost when power is turned off. It typically contains the firmware (like BIOS) needed to start the computer.
Cache Memory
A very high-speed, small-sized memory placed between the CPU and RAM. It stores frequently accessed data and instructions to speed up processing.
Secondary Storage
Non-volatile storage used for long-term storage of data and programs. It is slower but has a much larger capacity than primary memory.
- Hard Disk Drive (HDD): A magnetic storage device.
- Solid State Drive (SSD): Uses flash memory, much faster than an HDD.
- Optical Disks: CD, DVD, Blu-ray.
- Flash Drives: USB drives, memory cards.