Unit 1: Computer System
Complete Class 11 Computer Science Unit 1 notes in simple and easy-to-understand language for NEB students.
Welcome to Nepal eNotes. In this chapter, you will study the basic concepts of computers, computer generations, memory, processor, bus system, input/output devices and hardware interfaces.
These notes are organized lesson-by-lesson so that you can understand the chapter easily and revise it quickly before your examination.
- 1.1 Introduction to Computer
- 1.1.2 Evolution / Generation of Computer
- 1.1.3 Processing Speed & Storage Units
- 1.1.4 Types of Computer
- 1.1.5 Mobile Computing
- 1.2.1 Computer Architecture & Organization
- 1.2.2 Components of Computer System
- 1.2.3 Microprocessor
- 1.2.4 Bus System
- 1.2.5 Primary Memory
- 1.2.6 Secondary Memory
- 1.2.7 Input Devices
- 1.2.8 Output Devices
- 1.2.9 Hardware Interfaces
- Quick Revision
Definition of Computer
A computer is an electronic device that accepts raw data as input, processes it according to a set of instructions, produces meaningful information as output and stores the result for future use.
Input → Process → Output → Storage
Characteristics of Computer
⚡ Speed
A computer can perform millions or billions of operations within a very short period.
🎯 Accuracy
Computers can produce highly accurate results when correct data and instructions are provided.
🔄 Diligence
A computer does not become tired or bored and can repeat tasks with the same speed and accuracy.
💾 Storage
Computers can store large amounts of information and retrieve it whenever required.
🧩 Versatility
A single computer can perform many different types of tasks using different programs.
⚙ Automation
Once instructions are provided, a computer can automatically perform the assigned task.
Applications of Computer
- Education: Online classes, digital libraries and examinations.
- Business: Billing, accounting, inventory and payroll.
- Healthcare: Patient records, diagnosis and hospital management.
- Communication: Email, social media and video conferencing.
- Government: E-governance, national records and census processing.
- Entertainment: Games, movies, music and video editing.
- Science & Engineering: Research, simulations and designing.
- Security: Surveillance, navigation and security systems.
The development of computers is generally divided into five generations according to the major technology used.
| Generation | Technology | Main Features | Examples |
|---|---|---|---|
| First | Vacuum Tubes | Very large, produced high heat and used machine language. | ENIAC, UNIVAC |
| Second | Transistors | Smaller, faster and more reliable than vacuum-tube computers. | IBM 1401 |
| Third | Integrated Circuits | Smaller size, improved speed and use of high-level programming languages. | IBM 360 |
| Fourth | Microprocessor | Development of personal computers, laptops and modern systems. | PC, Laptop |
| Fifth | AI & ULSI | Artificial intelligence, machine learning and natural language processing. | AI Systems, Robotics |
Vacuum Tube → Transistor → IC → Microprocessor → AI
Processing Speed
Processor speed is generally measured in Hertz (Hz).
| Unit | Value |
|---|---|
| Hertz (Hz) | 1 cycle per second |
| Kilohertz (KHz) | 1,000 Hz |
| Megahertz (MHz) | 1,000,000 Hz |
| Gigahertz (GHz) | 1,000,000,000 Hz |
Storage Units
| Storage Unit | Equivalent |
|---|---|
| Bit | Smallest unit: 0 or 1 |
| Byte | 8 bits |
| Kilobyte (KB) | 1024 Bytes |
| Megabyte (MB) | 1024 KB |
| Gigabyte (GB) | 1024 MB |
| Terabyte (TB) | 1024 GB |
| Petabyte (PB) | 1024 TB |
Supercomputer
A supercomputer is the fastest and most powerful type of computer. It is used for extremely complex calculations.
Uses: Weather forecasting, scientific research and simulations.
Mainframe Computer
A mainframe is a large and powerful computer capable of supporting hundreds or thousands of users.
Uses: Banking, airlines, government organizations and large companies.
Minicomputer
A minicomputer is more powerful than a microcomputer but less powerful than a mainframe computer.
Microcomputer
A microcomputer is designed mainly for individual use.
Examples: Desktop computer, laptop, tablet and smartphone.
Supercomputer > Mainframe > Minicomputer > Microcomputer
Mobile computing is a technology that allows data, voice and video to be transmitted using portable wireless-enabled devices without requiring a fixed wired connection.
Elements of Mobile Computing
- Mobile Hardware: Smartphones, tablets, laptops and wearable devices.
- Mobile Communication: Wi-Fi, Bluetooth, 4G and 5G.
- Mobile Software: Applications and software running on mobile devices.
Applications
- Mobile banking and digital wallets
- GPS navigation
- Online learning
- Social media
- Instant messaging
- Cloud storage
- Remote working
- Mobile health monitoring
Computer architecture describes what a computer system does from the programmer’s point of view.
Computer organization describes how the computer’s hardware components are physically arranged and implemented.
| Computer Architecture | Computer Organization |
|---|---|
| Deals with what the system does. | Deals with how the system works. |
| Visible to programmers. | Mainly related to hardware design. |
| Example: Instruction set. | Example: Control signals and circuits. |
⌨ Input Unit
Accepts data and instructions from the user.
Examples: Keyboard, mouse and scanner.🧠 Processing Unit
The CPU processes instructions and controls computer operations.
💾 Memory Unit
Temporarily stores data and instructions required by the processor.
🗄 Storage Unit
Permanently stores programs, documents and files.
🖥 Output Unit
Presents processed information to the user.
A microprocessor is a single integrated circuit that contains the arithmetic, logical and control circuitry required to perform CPU functions.
Clock Speed
Clock speed is the rate at which a processor performs processing cycles. It is generally measured in MHz or GHz.
Word Length
Word length is the number of bits that a processor can process or transfer in a single operation.
Common word lengths include 8-bit, 16-bit, 32-bit and 64-bit.
Main Components of Microprocessor
ALU
Arithmetic Logic Unit performs arithmetic and logical operations.
Control Unit
Controls and coordinates the activities of different components.
Registers
Very small and fast storage locations inside the CPU.
Functions of Microprocessor
- Fetch instructions from memory.
- Decode instructions.
- Execute instructions.
- Perform arithmetic and logical operations.
- Control system operations.
- Communicate with memory and I/O devices.
A bus is a set of electrical pathways that transfers data, addresses and control signals between computer components.
Data Bus
Carries actual data between the CPU, memory and I/O devices.
Direction: Bi-directional.
Address Bus
Carries the address of the memory location where data will be read or written.
Direction: Uni-directional.
Control Bus
Carries control and timing signals such as read, write, interrupt and clock signals.
Data Bus = Data
Address Bus = Address
Control Bus = Control Signals
Primary memory is the main memory that can be directly accessed by the CPU.
RAM – Random Access Memory
RAM is volatile memory. Its contents are lost when the computer is switched off.
| RAM Type | Description |
|---|---|
| SRAM | Faster and more expensive. Commonly used for cache memory. |
| DRAM | Slower and cheaper. Commonly used as main system RAM. |
ROM – Read Only Memory
ROM is non-volatile memory. Its contents remain available even when the power is turned off.
| ROM Type | Description |
|---|---|
| PROM | Can be programmed once. |
| EPROM | Can be erased using ultraviolet light. |
| EEPROM | Can be erased and rewritten electrically. |
Cache Memory
Cache is a small and very fast memory placed close to the CPU. It stores frequently accessed data and instructions.
Buffer
A buffer is temporary storage used while data is being transferred between devices operating at different speeds.
Secondary memory is non-volatile storage used for permanently storing files, programs and data.
- Magnetic Disk: Hard Disk Drive (HDD).
- Flash Memory: SSD, USB drive and memory card.
- Optical Disk: CD, DVD and Blu-ray.
- External Storage: External HDD and external SSD.
- Memory Stick: Small portable flash-memory storage device.
Input devices are used to enter data and instructions into a computer.
| Device | Function |
|---|---|
| Keyboard | Enters text, numbers and commands. |
| Mouse | Points, selects and controls objects. |
| Scanner | Converts printed documents into digital form. |
| Light Pen | Used for pointing, selecting or drawing on compatible screens. |
| OMR | Reads marked answer sheets. |
| OCR | Converts printed or handwritten characters into digital text. |
| BCR | Reads barcodes. |
| MICR | Reads magnetic-ink characters, commonly used in banking. |
| Touch Screen | Allows interaction by touching the display. |
| Microphone | Captures voice and sound. |
| Digital Camera | Captures digital images and videos. |
Output devices convert processed information into a form that can be understood by the user.
Monitor
- LCD: Uses liquid crystal technology.
- LED: Uses LED backlighting for improved brightness and efficiency.
Printer
- Dot Matrix: Impact printer that uses pins and an ink ribbon.
- Inkjet: Sprays small droplets of ink onto paper.
- Laser: Uses laser technology and toner for fast, high-quality printing.
Speaker
A speaker converts electrical audio signals into audible sound.
A hardware interface or port is a connection point that allows external devices to communicate with a computer.
Parallel Port
Transfers multiple bits simultaneously and was traditionally used for printers.
Serial Port
Transfers data one bit at a time.
USB Port
USB stands for Universal Serial Bus. It is widely used to connect keyboards, mice, storage devices, printers and other peripherals.
HDMI
HDMI stands for High-Definition Multimedia Interface. It can transmit high-quality digital video and audio through a single connection.
Expansion Slots
Expansion slots are motherboard slots used to install additional cards.
- Graphics card
- Sound card
- Network card
⚡ Quick Revision – Unit 1
- Computer cycle: Input → Process → Output → Storage.
- Main characteristics: speed, accuracy, diligence, storage, versatility and automation.
- Five generations: Vacuum Tube → Transistor → IC → Microprocessor → AI .
- 1 Byte = 8 bits.
- 1 KB = 1024 Bytes.
- Processing speed is measured in Hz, MHz and GHz.
- Power order: Supercomputer > Mainframe > Minicomputer > Microcomputer .
- CPU mainly contains ALU + Control Unit + Registers.
- Main buses: Data, Address and Control Bus.
- Data Bus is bi-directional.
- Address Bus is uni-directional.
- RAM is volatile.
- ROM is non-volatile.
- RAM types: SRAM and DRAM.
- ROM types: PROM, EPROM and EEPROM.
Frequently Asked Questions
A computer is an electronic device that accepts data, processes it according to instructions, produces output and stores information.
The main components are the input unit, output unit, CPU, primary memory and secondary storage.
The three major buses are Data Bus, Address Bus and Control Bus.
RAM is volatile memory and loses its contents when power is turned off. ROM is non-volatile and retains its contents.
The major CPU components are the Arithmetic Logic Unit (ALU), Control Unit (CU) and Registers.
Secondary memory is non-volatile storage used for storing data and programs permanently. Examples include HDD, SSD, memory cards and USB drives.
Conclusion
Unit 1: Computer System introduces the fundamental concepts required to understand how computers work.
Make sure you understand computer generations, processor, memory, buses, input/output devices and hardware interfaces because these concepts are important for both examinations and later chapters.
Keep learning with Nepal eNotes for more Class 11 Computer Science notes, solutions and exam preparation materials.
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