Class 11: Computer Science : Computer System (Working Hour 20)

Class 11: Computer Science : Computer System (Working Hour 20)

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📘 Computer System – Detailed Notes (Class 11, Nepal Curriculum)

Contents
  1. 1.1 Introduction to Computer
  2. 1.2 Evolution of Computer
  3. 1.3 Measurement Units
  4. 1.4 Classification of Computers
  5. 1.5 Mobile Computing
  6. 1.6 Computer Architecture & Organization
  7. 1.7 Components of a Computer System
  8. 1.8 Microprocessor & Bus System
  9. 1.9 Primary & Secondary Memory
  10. 1.10 Input & Output Devices
  11. 1.11 Hardware Interfaces

1.1 Introduction to Computer

Definition

A computer is an electronic machine. It takes input from the user, processes the data, stores information, and gives output in a useful form. It works very fast and gives accurate results. A computer can do the same work again and again without getting tired.

Characteristics / Features

  • Accuracy: Produces correct results if the program and data are correct (GIGO principle applies).
  • Automatic: After starting a program, it runs with minimal human intervention.
  • Diligence:  Performs task for long time without getting tired with the same accuracy.
  • Speed: Executes millions to billions of instructions per second, solving complex tasks rapidly.
  • Storage: Stores vast data and retrieves it quickly when needed.
  • Versatility: Suitable for arithmetic, graphics, communication, simulations, and more.

Applications/ Working areas

  • Education: e‑learning, virtual classrooms, online examinations.
  • Business: billing, accounting, inventory control, e‑commerce.
  • Science & Engineering: simulations, data analysis, robotics, weather forecasting.
  • Entertainment: games, movies, music production, social media.
  • Communication: email, instant messaging, video conferencing.

1.2 Evolution of Computer

(A) Mechanical Era

  • Abacus (c. 3000 BC): It is the first calculating device. Early counting frame used for basic arithmetic invented in china later on became populer in asia region.It consists of two different parts, Upper part(Haven) which denots 5 and Lower part(Earth) which denotes 1.

  • Nepier's Bone: Invented by John Napier in 1617 AD. It was a calculating device made of rods marked with numbers. It was mainly used for multiplication and division. This device made calculations faster and easier before modern calculators were developed.

  • Slide Rule: Invented by William Oughtred in 1622. It is based on the principle of logarithms. It looks like a ruler with sliding parts and was used to perform multiplication, division, square roots, and trigonometry. Scientists and engineers used it widely before electronic calculators came.It is also known as the first analog device.

  • Pascaline (1642): Blaise Pascal’s gear‑based adder/subtracter built to aid calculations. It is also known as first mechanical calculator.

  • Leibniz Calculator (1673): Also know as stepped reckoner Invented by Gottfried Wilhelm von Leibniz Improved mechanical calculator performing multiplication and division. 

  • Difference Engine (1822): Charles Babbage’s steam‑powered design for polynomial tables. It was started with funding from us government in cambridge Universtity. He is also know as the Father of Modern computer. 

  • Analytical Engine (1837): Babbage’s general‑purpose design with concept of ALU, control, memory, and I/O. The same concept has been used to desing and build today's computer that's why he is known as father of modern computer.

  • Lady Augusta Ada: Lady Augusta Ada Lovelace (1815–1852) was the first computer programmer. She worked with Charles Babbage on the Analytical Engine. She wrote the first algorithm that could be executed by a machine. Because of this, she is remembered as the mother of computer programming.

  • Tabulating Machine: Invented by Herman Hollerith in 1890. It was designed to process and analyze data stored in punched cards. Hollerith first used it in the U.S. Census of 1890, which reduced the time to complete the census from 10 years to just 3 years. The machine could count, sort, and summarize data quickly. This invention laid the foundation for modern data processing machines and led to the establishment of the company that later became IBM (International Business Machines).

(B) Electro‑Mechanical Era

  • Zuse Z3 (1941)

    • Invented by Konrad Zuse (Germany)

    • First programmable digital computer

    • Worked with electromechanical relays

  • Harvard MARK I (1944)

    • Invented by Howard Aiken with support from IBM

    • Large electromechanical computer

    • Used in U.S. Navy for ballistic calculations

  • Harvard MARK II (1947)

    • Improved version of MARK I

    • Still electromechanical

    • Known for the term "computer bug" (moth stuck in relay)

  • Atanasoff–Berry Computer (ABC) (1937–42)

    • Built by John Atanasoff and Clifford Berry

    • Used vacuum tubes for processing (electronic) but also had mechanical parts for memory

(C) Electronic Era

  • ENIAC (1946): First general‑purpose electronic computer using vacuum tubes; very large and power‑hungry.
  • EDVAC (1949): Early stored‑program concept that influenced future designs.
  • UNIVAC I (1951): First commercially available computer used for business and government.

Generations of Computers

Generation Period Main Technology Size Speed Cost Input/Output System Programming Language Electricity Consumption
1st Gen 1940–1956 Vacuum Tubes Very Large Milliseconds Very High Punched cards, Paper tape Machine language Very High
2nd Gen 1956–1963 Transistors Smaller Microseconds High Punch cards, Magnetic tape Assembly language High
3rd Gen 1964–1971 Integrated Circuits (IC) Small Nanoseconds Lower Keyboard, Monitor High‑level languages Medium
4th Gen 1971–Present Microprocessors Smaller Picoseconds Affordable GUI, Mouse, Printer 4GL, OOP Low
5th Gen Present & Beyond AI, Robotics, Quantum Very Small Femtoseconds Variable Natural language, Voice AI/ML/NLP Very Low

1.3 Measurement Units

Processing Speed

  • Second (s)
  • Millisecond (ms) = 10−3 s
  • Microsecond (µs) = 10−6 s
  • Nanosecond (ns) = 10−9 s
  • Picosecond (ps) = 10−12 s
  • Femtosecond (fs) = 10−15 s

Storage Units

  • 0,1   = bit

  • 1 Byte (B) = 8 Bits

  • 1 Kilobyte (KB) = 1024 Bytes

  • 1 Megabyte (MB) = 1024 Kilobytes

  • 1 Gigabyte (GB) = 1024 Megabytes

  • 1 Terabyte (TB) = 1024 Gigabytes

  • 1 Petabyte (PB) = 1024 Terabytes

  • 1 Exabyte (EB) = 1024 Petabytes

  • 1 Zettabyte (ZB) = 1024 Exabytes

  • 1 Yottabyte (YB) = 1024 Zettabytes

1.4 Classification of Computers

Based on Nature of Task

  • Analog Computers: Measure continuous physical quantities (e.g., temperature, speed). Example: analog speedometer. Seismograph
  • Digital Computers: Operate on discrete binary data (0/1) or we can say this type of computer processes discontinuous or discrete data. Examples: PCs, laptops, smartphones.
  • Hybrid Computers: Combine analog measurement with digital processing. Example: ICU/ECG systems.

Types of Digital Computers

  • Microcomputer: Single‑user systems having single microprocessor  like desktops and laptops; used at home, school, and office.
  • Minicomputer: Mid‑range, supports multiple users; used in institutes and SMEs (e.g., PDP series).
  • Mainframe: High‑performance systems handling massive I/O (e.g., IBM Z‑series) for banks/airlines.
  • Supercomputer: Extremely fast; used in weather simulation, AI, and scientific research (e.g., Fugaku).

1.5 Mobile Computing

Mobile computing enables data, voice, and video communication using portable devices (smartphones, tablets, laptops) over wireless networks (Wi‑Fi, cellular). It supports mobility, context awareness (GPS), and real‑time access to cloud services.

Applications

  • GPS navigation and ride‑hailing
  • Online banking and payments
  • E‑commerce and social media
  • Cloud apps and collaboration

1.6 Computer Architecture & Organization

Architecture is the functional design (what components do and how they interact). Organization is the implementation detail (how signals, buses, and control lines are realized).

Working Cycle (IPO + Storage)

Input CPU / Process Output Storage Stored programs & data feed processing
Input → Processing → Output with persistent Storage (stored‑program concept).

Explanation: Data enters via input devices, the CPU (ALU + Control Unit + Registers) processes it using instructions stored in memory, results are presented through output devices, and data/instructions persist in storage for later use.

1.7 Components of a Computer System

  • Hardware: Physical parts (CPU, motherboard, monitor, keyboard, printer).
  • Software: System software (Operating System) and application software (word processor, browser).

1.8 Microprocessor & Bus System

Microprocessor: CPU on a single chip that performs arithmetic/logic operations, controls instructions, and coordinates system activities (e.g., Intel Core i5/i7, AMD Ryzen).

Bus System: Shared pathways for communication among CPU, memory, and I/O:

  • Data Bus: Carries actual data.
  • Address Bus: Specifies memory/I-O addresses.
  • Control Bus: Carries control signals (read/write, clock, interrupts).
CPU Primary Memory I/O Devices Storage Address/Data/Control Buses
CPU communicates with Memory, I/O, and Storage via address, data, and control buses.

1.9 Primary & Secondary Memory

Primary Memory

  • RAM: Volatile, temporary workspace for running programs and data. Types: SRAM and DRAM
  • ROM: Non‑volatile, stores firmware/boot instructions. Types of ROM are PROM, EPROM, EEPROM

Secondary Memory

  • Magnetic disks (HDD)
  • Solid State Drives (SSD), Flash (USB drives)
  • Optical media (CD/DVD)
Storage (HDD/SSD) Main Memory (RAM) Cache Registers ↑ Speed / Cost per bit | Capacity ↓
Memory hierarchy: registers → cache → RAM → storage.

1.10 Input & Output Devices

Input Devices

  • Keyboard: Numeric keys, alphabetic keys, function keys (F1–F12), control/navigation keys.
  • Mouse: Pointing device with buttons and scroll wheel.
  • Joystick, scanner, microphone, touch screen, webcam.

Output Devices

Softcopy: Monitor (CRT, LCD, LED), speaker, projector.

Hardcopy: Printer and plotter.

  • Printer types & mechanism:
    • Dot‑matrix: Impact pins strike ink ribbon to form dots (noisy, multipart forms).
    • Inkjet: Sprays tiny ink droplets (good color/photo prints).
    • Laser: Uses laser + toner with electro‑photography (fast, sharp text).
  • Plotter: Vector graphics for large engineering drawings; pen or thermal/cutter based.

1.11 Hardware Interfaces

Definition: Standard connection points and protocols that allow devices to communicate with a computer.

  • USB (Universal Serial Bus): General‑purpose port for keyboards, mice, storage, cameras.
  • HDMI (High‑Definition Multimedia Interface): Digital audio/video output to monitors/TVs/projectors.
  • VGA (Video Graphics Array): Legacy analog video connector.
  • Ethernet (RJ‑45): Wired LAN networking.
  • Serial Port (RS‑232): Sends data one bit at a time; used for modems/industrial devices.
  • Parallel Port (DB‑25): Multiple bits simultaneously; historically used for printers.

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Sandesh Shiwakoti

Written By

Sandesh Shiwakoti

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