Basic Computer Organisation Class 11 CBSE Computer Science: Introduction to Computer System, Hardware, Software, CPU, Memory and Units of Memory
Class 11 · Computer Science
Basic Computer Organisation (CBSE Class 11 Computer Science)
A computer system is an electronic device that accepts data as input, processes it according to a set of instructions, stores the processed information, and produces meaningful output. Every computer, whether it is a smartphone, laptop, desktop, or supercomputer, follows the same basic working principle known as the Input-Process-Output (IPO) Cycle.
Learning Objectives
- Understand the concept of a computer system.
- Learn the basic organisation of a computer.
- Differentiate between hardware and software.
- Understand input and output devices.
- Study the Central Processing Unit (CPU).
- Learn about different types of memory.
- Understand units of memory.
What is a Computer System?
A computer system is a combination of hardware and software that works together to perform various tasks such as calculations, data processing, communication, and information storage.
Basic Organisation of a Computer System
+------------------+
| Input Devices |
+------------------+
│
▼
+------------------+
| CPU |
| (Processing Unit)|
+------------------+
│
┌──────────┴──────────┐
▼ ▼
+----------------+ +----------------+
| Primary Memory | | Secondary |
| (RAM / ROM) | | Storage |
+----------------+ +----------------+
│
▼
+------------------+
| Output Devices |
+------------------+
Components of a Computer System
A computer system consists of the following major components:
- Hardware
- Software
- Input Devices
- Central Processing Unit (CPU)
- Memory
- Output Devices
Hardware
Hardware refers to the physical components of a computer that can be seen and touched.
Examples
- Keyboard
- Mouse
- Monitor
- CPU Cabinet
- Printer
- Scanner
- Hard Disk
Software
Software is a collection of programs and instructions that tell the computer how to perform specific tasks.
Examples
- Windows
- Linux
- MS Word
- Python
- Google Chrome
Difference Between Hardware and Software
| Hardware | Software |
|---|---|
| Physical components. | Collection of programs. |
| Can be touched. | Cannot be touched. |
| May wear out over time. | Does not wear out physically. |
| Manufactured. | Developed or programmed. |
Input Devices
Input devices are used to enter data and instructions into the computer.
Common Input Devices
| Device | Purpose |
|---|---|
| Keyboard | Enter text and numbers. |
| Mouse | Select and control objects. |
| Scanner | Convert paper documents into digital form. |
| Microphone | Input voice. |
| Web Camera | Capture images and videos. |
| Barcode Reader | Read barcodes. |
Output Devices
Output devices display the processed information to the user.
Common Output Devices
| Device | Purpose |
|---|---|
| Monitor | Displays visual output. |
| Printer | Produces hard copies. |
| Speaker | Produces sound output. |
| Projector | Displays output on a large screen. |
| Plotter | Prints engineering drawings. |
Central Processing Unit (CPU)
The Central Processing Unit (CPU) is known as the brain of the computer. It performs calculations, executes instructions, and controls all operations of the computer.
Main Components of CPU
- Arithmetic Logic Unit (ALU)
- Control Unit (CU)
- Registers
Arithmetic Logic Unit (ALU)
The ALU performs arithmetic operations and logical comparisons.
Arithmetic Operations
- Addition
- Subtraction
- Multiplication
- Division
Logical Operations
- AND
- OR
- NOT
- Comparison (>, <, =)
Control Unit (CU)
The Control Unit coordinates all activities of the computer. It controls the flow of data between the CPU, memory, and input/output devices.
Registers
Registers are very small and extremely fast memory locations inside the CPU. They temporarily store data and instructions currently being processed.
Memory
Memory is the storage area of a computer where data, instructions, and results are stored.
Types of Memory
- Primary Memory
- Cache Memory
- Secondary Memory
Primary Memory
Primary memory is directly accessible by the CPU and stores data that is currently being processed.
Types
- RAM (Random Access Memory)
- ROM (Read Only Memory)
Characteristics
- Fast access.
- Limited capacity.
- Expensive.
- RAM is volatile.
Cache Memory
Cache memory is a very high-speed memory located between the CPU and primary memory. It stores frequently used data and instructions, reducing access time.
Characteristics
- Fastest memory after registers.
- Very expensive.
- Small storage capacity.
Secondary Memory
Secondary memory stores data permanently and retains information even after the computer is switched off.
Examples
- Hard Disk
- SSD
- CD/DVD
- Pen Drive
- Memory Card
Comparison of Memory Types
| Feature | Primary | Cache | Secondary |
|---|---|---|---|
| Speed | Fast | Very Fast | Slow |
| Capacity | Medium | Very Small | Very Large |
| Cost | High | Very High | Low |
| Volatile | Yes (RAM) | Yes | No |
Units of Memory
Computers store information in the form of binary digits (0 and 1). Different units are used to measure memory capacity.
| Unit | Equivalent |
|---|---|
| 1 Bit | 0 or 1 |
| 1 Byte | 8 Bits |
| 1 KB | 1024 Bytes |
| 1 MB | 1024 KB |
| 1 GB | 1024 MB |
| 1 TB | 1024 GB |
| 1 PB | 1024 TB |
Memory Hierarchy
Registers
│
▼
Cache Memory
│
▼
Primary Memory (RAM)
│
▼
Secondary Storage
As we move down the hierarchy:
- Storage capacity increases.
- Cost per bit decreases.
- Access speed decreases.
Real-Life Example
Think of a student studying for an exam:
- Registers are like the information currently in your mind.
- Cache Memory is like notes kept on your study table.
- RAM is like the books currently opened while studying.
- Secondary Memory is like books stored on a bookshelf.
Common Errors
- Confusing hardware with software.
- Assuming CPU and CPU cabinet are the same.
- Confusing RAM with secondary storage.
- Thinking cache memory stores data permanently.
- Using decimal values (1000) instead of binary values (1024) for memory units in CBSE questions.
Exam Tips
- Remember the IPO (Input-Process-Output) cycle.
- CPU consists of ALU, CU, and Registers.
- Cache memory is faster than RAM.
- Secondary memory is non-volatile.
- Learn the memory unit conversions up to Petabyte.
- Be able to compare Primary, Cache, and Secondary memory.
Frequently Asked Questions (FAQs)
1. Why is the CPU called the brain of the computer?
The CPU performs calculations, executes instructions, and controls all computer operations.
2. What is the difference between RAM and ROM?
RAM is volatile and stores temporary data, whereas ROM is non-volatile and stores permanent instructions.
3. Which memory is faster: Cache or RAM?
Cache memory is faster than RAM.
4. What is the smallest unit of memory?
The bit (Binary Digit) is the smallest unit of memory.
5. What is the relationship between Byte and Bit?
One Byte consists of 8 Bits.
Summary
- A computer system consists of hardware and software working together.
- The IPO cycle explains how a computer accepts input, processes data, and produces output.
- The CPU contains the ALU, Control Unit, and Registers.
- Memory is classified into Primary Memory, Cache Memory, and Secondary Memory.
- Cache memory is faster than RAM, while secondary memory provides permanent storage.
- Memory capacity is measured using units such as Bit, Byte, KB, MB, GB, TB, and PB.
- Understanding the organisation of a computer system is the foundation for learning Computer Science.