CBSE Class 11 Computer Science (083)
Unit 1: Computer Systems and Organisation
Complete Easy Notes | Session 2026–27
Unit Overview
A computer is an electronic machine that accepts data, processes it according to instructions, stores information and produces useful output.
This unit explains how a computer is organised, how hardware and software work together, how an operating system manages resources, how Boolean logic works, how numbers are represented inside computers, and how text is encoded digitally.
1. Introduction to Computer System
What is a Computer?
A computer is an electronic programmable device that accepts data as input, processes it according to a set of instructions, stores data/results and produces output.
Basic Working of a Computer
┌───────────────┐
│ INPUT │
│ Keyboard etc. │
└───────┬───────┘
↓
┌───────────────┐
│ PROCESSING │
│ CPU │
└───────┬───────┘
↓
┌───────────────┐
│ OUTPUT │
│ Monitor etc. │
└───────────────┘
↑
│
┌───────┴───────┐
│ MEMORY │
│ Store data & │
│ instructions │
└───────────────┘
Four Basic Operations
A computer generally performs four major operations:
Input – accepts data and instructions.
Processing – performs calculations and logical operations.
Output – presents the result.
Storage – stores data, instructions and results.
Example
Suppose we calculate:
25 + 15
Keyboard
↓
25 + 15
↓
CPU processes the calculation
↓
40
↓
Monitor
Here:
Keyboard = Input
CPU = Processing
Monitor = Output
Memory/storage = Stores required data and instructions
2. Computer System Components
A computer system mainly consists of:
COMPUTER SYSTEM
│
┌────────────┴────────────┐
↓ ↓
HARDWARE SOFTWARE
│ │
┌────┴─────┐ ┌────┴────────┐
↓ ↓ ↓ ↓
Input/Output CPU System Application
Devices Software Software
│
┌──────┴──────┐
↓ ↓
Memory ALU/CU
3. Hardware
Definition
Hardware refers to the physical parts of a computer system that can be seen and touched.
Examples
Keyboard
Mouse
Monitor
CPU cabinet
Printer
Scanner
Speakers
Hard disk/SSD
RAM
Motherboard
Webcam
Easy Definition
Hardware = Physical parts of a computer.
4. Software
Definition
Software is a collection of programs and related instructions that tell a computer what to do.
Software cannot normally be physically touched.
Examples
Windows
Linux
Android
MS Word
Python
Web browsers
Media players
Easy Definition
Software = Set of instructions/programs used to operate a computer.
5. Hardware vs Software
| Hardware | Software |
|---|---|
| Physical component | Program/instructions |
| Can be touched | Cannot be physically touched |
| May be damaged physically | May be corrupted/deleted |
| Keyboard is hardware | Windows is software |
| Monitor is hardware | Python is software |
Remember
Hardware needs software to perform useful tasks, and software needs hardware to execute.
6. Input Devices
Definition
An input device is a hardware device used to enter data or instructions into a computer.
Common Input Devices
| Device | Main Use |
|---|---|
| Keyboard | Enter text and commands |
| Mouse | Point, select and control objects |
| Scanner | Convert paper documents/images into digital form |
| Microphone | Enter sound |
| Webcam | Capture images/video |
| Touchscreen | Accept touch input |
| Barcode Reader | Read barcodes |
| Joystick | Control games/simulations |
Example
When you type your name using a keyboard, the keyboard acts as an input device.
7. Output Devices
Definition
An output device presents processed information from a computer to the user.
Common Output Devices
| Device | Main Use |
|---|---|
| Monitor | Displays text/images/video |
| Printer | Produces hard copy |
| Speakers | Produce sound |
| Projector | Displays computer output on a large screen |
| Headphones | Produce audio for the user |
Soft Copy and Hard Copy
Soft copy: Information displayed electronically.
Example: Information displayed on a monitor.
Hard copy: Information printed on paper.
Example: Printed report.
8. Central Processing Unit (CPU)
The CPU (Central Processing Unit) is the main processing unit of a computer. It executes instructions and performs calculations and logical operations.
It is often called the brain of the computer, although technically it is the processor that executes instructions while the complete computer system includes many other components.
Main Components of CPU
CPU
│
┌───────┼────────┐
↓ ↓ ↓
ALU CU Registers
│ │ │
Arithmetic Control Very fast
& Logic signals storage
9. ALU
ALU stands for Arithmetic Logic Unit.
It performs:
Arithmetic Operations
Addition
Subtraction
Multiplication
Division
Logical Operations
Comparison
AND
OR
NOT
Other logical operations
Example
For:
20 > 10
The ALU can perform the comparison and determine that the statement is true.
10. Control Unit (CU)
The Control Unit (CU) controls and coordinates the activities of the computer.
It:
Fetches instructions.
Decodes instructions.
Directs other components.
Controls the execution sequence.
Coordinates data movement.
Simple Flow
Instruction
↓
Fetch
↓
Decode
↓
Execute
↓
Result
11. Registers
Registers are very small and very fast storage locations inside the CPU.
They temporarily hold:
Data
Instructions
Addresses
Intermediate results
Registers are generally faster than main memory.
12. Memory
Memory is used to store:
Data
Instructions
Intermediate results
Final results
Computer memory can broadly be classified as:
MEMORY
│
┌────────┴────────┐
↓ ↓
PRIMARY SECONDARY
MEMORY MEMORY
│
┌────┴────┐
↓ ↓
RAM ROM
Cache memory is a very fast memory placed close to/within the processor-memory hierarchy to reduce the time needed to access frequently required data and instructions.
13. Primary Memory
Primary memory is the main memory directly used by the CPU during processing.
Important examples include:
RAM
ROM
RAM
RAM = Random Access Memory
RAM stores programs and data currently being used.
Characteristics of RAM
Fast
Read/write memory
Generally volatile
Contents are normally lost when power is removed
Example
When you open a browser, its currently running program and data are loaded into RAM.
14. ROM
ROM = Read Only Memory
ROM stores information that is intended to remain available even when power is switched off.
Modern systems can use different forms of non-volatile firmware storage, but the syllabus commonly introduces this concept as ROM.
Characteristics
Non-volatile
Retains information without power
Used for firmware/start-up instructions
15. Cache Memory
Cache memory is a small, high-speed memory used to reduce the average time required to access frequently needed data and instructions.
It is faster than normal RAM.
Memory Speed Concept
CPU Registers
↓
Cache
↓
RAM
↓
SSD/HDD
Generally, moving downward in this hierarchy gives larger storage capacity but slower access.
Why is Cache Used?
The CPU works extremely fast. If it had to wait for slower memory every time, processing would become less efficient.
Cache keeps frequently needed information closer to the CPU.
Example
If the CPU repeatedly needs the same instruction/data, cache may allow faster access.
16. Secondary Memory
Secondary memory is used for long-term storage of programs and data.
Examples:
HDD
SSD
Pen drive
Memory card
Optical disc
Characteristics
Non-volatile
Usually larger capacity than primary memory
Used for permanent/long-term storage
Generally slower than RAM
17. Primary vs Secondary Memory
| Primary Memory | Secondary Memory |
|---|---|
| Used directly during processing | Used mainly for long-term storage |
| Faster | Generally slower |
| Usually smaller capacity | Usually larger capacity |
| RAM is volatile | Secondary storage is generally non-volatile |
| More expensive per unit of storage | Usually cheaper per unit of storage |
18. Memory Hierarchy
A simplified memory hierarchy is:
FASTEST
↑
┌───────────┐
│ Registers │
├───────────┤
│ Cache │
├───────────┤
│ RAM │
├───────────┤
│ SSD / HDD │
└───────────┘
↓
LARGER
CAPACITY
Key Idea
Higher speed generally comes with smaller capacity and higher cost per unit of storage.
19. Units of Memory
Computers store information using binary digits.
Bit
Bit stands for Binary Digit.
A bit can have only two values:
0 or 1
1 bit → 0 or 1
Byte
1 Byte = 8 bits
1 Byte
= 8 bits
= 10101100
Common Memory Units
| Unit | Relationship |
|---|---|
| 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* |
For CBSE number-system questions, the binary convention of 1024 is commonly used.
Quick Ladder
bit
↓
Byte
↓
KB
↓
MB
↓
GB
↓
TB
↓
PB
Memory Conversion Example
2 KB = ? Bytes
1 KB = 1024 Bytes
Therefore:
2 KB = 2 × 1024
= 2048 Bytes
20. Types of Software
Software can broadly be classified into:
SOFTWARE
│
┌────────────┼─────────────┐
↓ ↓ ↓
System Software Programming Application
Tools &
Translators
21. System Software
System software controls and manages computer hardware and provides a platform for application programs.
Main examples in the syllabus:
Operating systems
System utilities
Device drivers
22. Operating System
An Operating System (OS) is system software that manages computer hardware and software resources and provides services to application programs and users.
Examples:
Windows
Linux
macOS
Android
iOS
23. System Utilities
System utilities are programs that help maintain, manage, protect or optimise a computer system.
Examples:
Backup utilities
Disk management tools
File compression tools
Antivirus/security utilities
System cleanup tools
24. Device Drivers
A device driver is system software that allows the operating system to communicate with and control a particular hardware device.
Examples
Printer driver
Graphics driver
Audio driver
Network adapter driver
Simple Diagram
Application
↓
Operating System
↓
Device Driver
↓
Hardware Device
25. Programming Tools and Language Translators
A computer's processor executes machine-level instructions.
Programming languages therefore need suitable translation tools.
Important translators:
Assembler
Compiler
Interpreter
26. Assembler
An assembler translates assembly language instructions into machine code.
Assembly Language
↓
ASSEMBLER
↓
Machine Code
Example concept:
MOV A, B
↓
Assembler
↓
Machine instructions
27. Compiler
A compiler translates a program written in a high-level language into lower-level/machine-oriented code before execution, depending on the language and compiler design.
A traditional compiler generally translates the program as a whole into an executable/object form.
High-Level Program
↓
COMPILER
↓
Object / Machine-oriented Code
↓
Execute
Advantages
Program can execute efficiently after successful compilation.
Errors can be reported during compilation.
The compiled program can often be run without translating the source again, subject to the language/toolchain.
28. Interpreter
An interpreter translates and executes program instructions progressively during execution.
Source Program
↓
INTERPRETER
↓
Instruction execution
↓
Next instruction
Python is commonly taught as an interpreted language in school-level contexts, although its actual implementation uses intermediate bytecode and a virtual machine.
Compiler vs Interpreter
| Compiler | Interpreter |
|---|---|
| Usually translates the program before execution | Translates/executes progressively |
| Produces object/executable output in many compiled toolchains | Usually does not produce a standalone machine-code executable as its primary output |
| Errors are generally reported after compilation stages | Errors can appear when the relevant statement/path is executed |
| Execution after compilation can be efficient | Repeated translation/execution can add overhead |
29. Application Software
Application software is designed to help users perform specific tasks.
Examples
| Application | Purpose |
|---|---|
| MS Word | Word processing |
| Spreadsheet software | Calculations and data analysis |
| Web browser | Access websites |
| Media player | Play multimedia |
| Presentation software | Create presentations |
| Photo editor | Edit images |
Easy Rule
System software runs/manages the computer; application software helps the user perform tasks.
30. Operating System – Functions
The operating system performs many important functions.
1. Process Management
The OS manages running programs/processes and allocates processor time to them.
2. Memory Management
It manages the allocation and release of memory for programs.
3. File Management
It helps create, store, organise, rename, copy and delete files and folders.
4. Device Management
It manages hardware devices through drivers and system services.
5. Security
It helps control access to resources using accounts, permissions and other security mechanisms.
6. User Interface
It provides a way for users to interact with the computer.
7. Resource Management
It coordinates resources such as:
CPU
Memory
Storage
Input/output devices
OS as Resource Manager
OPERATING SYSTEM
│
┌────────────┼────────────┐
↓ ↓ ↓
CPU Memory Devices
│ │ │
└────────────┼────────────┘
↓
Users
& Applications
31. OS User Interface
A user interface is the method through which a user communicates with the operating system.
Two important types are:
GUI
GUI = Graphical User Interface
It uses:
Windows
Icons
Menus
Pointer
Buttons
Dialog boxes
Example: Windows desktop environment.
Advantages
Easy for beginners
Visual interaction
Point-and-click operation
CLI
CLI = Command Line Interface
Users type commands to interact with the operating system.
Example:
C:\> dir
Advantages
Powerful for experienced users
Efficient for many administrative tasks
Useful for automation and scripting
GUI vs CLI
| GUI | CLI |
|---|---|
| Uses graphical elements | Uses typed commands |
| Easier for beginners | Requires command knowledge |
| Uses mouse/touch frequently | Mainly keyboard |
| Visual | Text-based |
32. Boolean Logic
Boolean logic is a system of logic in which values are generally represented as:
True/False
or
1/0
It is fundamental to digital computers and logic circuits.
Boolean Values
TRUE = 1
FALSE = 0
33. Boolean Operators
Important Boolean operators are:
NOT
AND
OR
NAND
NOR
XOR
34. NOT Gate
NOT gives the opposite value of the input.
Boolean Expression
Y = NOT A
or
Y = A̅
Truth Table
| A | NOT A |
|---|---|
| 0 | 1 |
| 1 | 0 |
Diagram
A ─────► [ NOT ] ─────► Y
35. AND Gate
AND gives output 1 only when all inputs are 1.
Boolean Expression
Y = A · B
Truth Table
| A | B | A AND B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Easy Rule
AND → All must be 1.
36. OR Gate
OR gives output 1 when at least one input is 1.
Boolean Expression
Y = A + B
Truth Table
| A | B | A OR B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Easy Rule
OR → Any one can be 1.
37. NAND Gate
NAND means:
NOT + AND
Therefore:
Y = NOT(A AND B)
or
Y = (A · B)̅
Truth Table
| A | B | AND | NAND |
|---|---|---|---|
| 0 | 0 | 0 | 1 |
| 0 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 0 |
Easy Rule
NAND is the opposite of AND.
38. NOR Gate
NOR means:
NOT + OR
Therefore:
Y = NOT(A OR B)
or
Y = (A + B)̅
Truth Table
| A | B | OR | NOR |
|---|---|---|---|
| 0 | 0 | 0 | 1 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 1 | 0 |
Easy Rule
NOR is the opposite of OR.
39. XOR Gate
XOR = Exclusive OR
XOR gives output 1 when the two inputs are different.
Boolean Expression
Y = A ⊕ B
Truth Table
| A | B | XOR |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Easy Rule
XOR → Different = 1, Same = 0.
40. Complete Boolean Truth Table
| A | B | NOT A | AND | OR | NAND | NOR | XOR |
|---|---|---|---|---|---|---|---|
| 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 0 | 1 | 1 | 0 | 1 |
| 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 |
Memory Trick
AND: Only 11 → 1
OR: Only 00 → 0
NAND: Opposite of AND
NOR: Opposite of OR
XOR: Different → 1
NOT: Reverse the input
41. Logic Circuits
A logic circuit is an electronic circuit made from logic gates that processes binary input signals to produce a binary output.
Example: AND Circuit
A ─────┐
│
├──► AND ───► Y
│
B ─────┘
Example: OR Circuit
A ─────┐
│
├──► OR ───► Y
│
B ─────┘
Combined Logic Circuit
Consider:
Y = (A AND B) OR C
A ─────┐
├──► AND ───┐
B ─────┘ │
├──► OR ───► Y
C ─────────────────┘
To solve such a circuit:
Solve the AND gate first.
Take its output with C.
Apply OR.
Obtain final output.
42. De Morgan's Laws
De Morgan's laws are important Boolean algebra rules.
First Law
NOT (A AND B) = (NOT A) OR (NOT B)
Symbolically:
(A · B)̅ = A̅ + B̅
Meaning
The complement of AND becomes OR of the complements.
Second Law
NOT (A OR B) = (NOT A) AND (NOT B)
Symbolically:
(A + B)̅ = A̅ · B̅
Meaning
The complement of OR becomes AND of the complements.
43. Easy Way to Remember De Morgan's Laws
When applying De Morgan's laws:
Rule 1
AND changes to OR
Rule 2
OR changes to AND
Rule 3
Each variable is complemented
AND ↔ OR
↓ ↓
NOT each input
44. Number System
A number system is a method of representing numbers using a particular set of symbols and a base (radix).
Important number systems:
Decimal
Binary
Octal
Hexadecimal
45. Decimal Number System
The decimal system has base 10.
It uses:
0 1 2 3 4 5 6 7 8 9
Example
572
5 × 10² + 7 × 10¹ + 2 × 10⁰
= 500 + 70 + 2
= 572
46. Binary Number System
The binary system has base 2.
It uses only:
0 and 1
Computers use binary representation because digital electronic circuits can represent two distinct states.
Example
Binary number:
1011₂
Its decimal value is:
1×2³ + 0×2² + 1×2¹ + 1×2⁰
= 8 + 0 + 2 + 1
= 11₁₀
47. Octal Number System
The octal system has base 8.
It uses:
0 1 2 3 4 5 6 7
Example
725₈
7×8² + 2×8¹ + 5×8⁰
= 448 + 16 + 5
= 469₁₀
48. Hexadecimal Number System
The hexadecimal system has base 16.
It uses:
0 1 2 3 4 5 6 7 8 9 A B C D E F
Here:
A = 10
B = 11
C = 12
D = 13
E = 14
F = 15
Example
2A₁₆
2×16¹ + A×16⁰
= 2×16 + 10×1
= 32 + 10
= 42₁₀
49. Number System Comparison
| Number System | Base | Digits |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0–7 |
| Decimal | 10 | 0–9 |
| Hexadecimal | 16 | 0–9, A–F |
Important Shortcut
Binary → Base 2
Octal → Base 8
Decimal → Base 10
Hexadecimal → Base 16
50. Binary to Decimal Conversion
Example
Convert:
1101₂ → Decimal
Write powers of 2 from right to left:
1 1 0 1
↓ ↓ ↓ ↓
2³ 2² 2¹ 2⁰
Now:
1×8 + 1×4 + 0×2 + 1×1
= 8 + 4 + 0 + 1
= 13
Therefore:
1101₂ = 13₁₀
51. Decimal to Binary Conversion
Use repeated division by 2.
Example
Convert 13₁₀ to binary.
13 ÷ 2 = 6 remainder 1
6 ÷ 2 = 3 remainder 0
3 ÷ 2 = 1 remainder 1
1 ÷ 2 = 0 remainder 1
Read remainders from bottom to top:
1101
Therefore:
13₁₀ = 1101₂
Golden Rule
Decimal to binary → Divide by 2 repeatedly and read remainders from bottom to top.
52. Decimal to Octal Conversion
Use repeated division by 8.
Example
Convert 83₁₀ to octal.
83 ÷ 8 = 10 remainder 3
10 ÷ 8 = 1 remainder 2
1 ÷ 8 = 0 remainder 1
Read upward:
123₈
Therefore:
83₁₀ = 123₈
53. Octal to Decimal Conversion
Example
Convert 123₈ to decimal.
1×8² + 2×8¹ + 3×8⁰
= 64 + 16 + 3
= 83
Therefore:
123₈ = 83₁₀
54. Decimal to Hexadecimal Conversion
Use repeated division by 16.
Example
Convert 42₁₀ to hexadecimal.
42 ÷ 16 = 2 remainder 10
10 = A
Therefore:
42₁₀ = 2A₁₆
55. Hexadecimal to Decimal Conversion
Example
Convert 2A₁₆ to decimal.
2×16¹ + A×16⁰
= 2×16 + 10×1
= 32 + 10
= 42
Therefore:
2A₁₆ = 42₁₀
56. Binary to Octal Conversion
Group binary digits into groups of 3 from the right.
Example
Convert:
101101₂
Group:
101 101
Now:
101₂ = 5
101₂ = 5
Therefore:
101101₂ = 55₈
Useful Table
| Binary | Octal |
|---|---|
| 000 | 0 |
| 001 | 1 |
| 010 | 2 |
| 011 | 3 |
| 100 | 4 |
| 101 | 5 |
| 110 | 6 |
| 111 | 7 |
57. Binary to Hexadecimal Conversion
Group binary digits into groups of 4 from the right.
Example
Convert:
10101110₂
Group:
1010 1110
Now:
1010 = A
1110 = E
Therefore:
10101110₂ = AE₁₆
Important Table
| Binary | Hex |
|---|---|
| 0000 | 0 |
| 0001 | 1 |
| 0010 | 2 |
| 0011 | 3 |
| 0100 | 4 |
| 0101 | 5 |
| 0110 | 6 |
| 0111 | 7 |
| 1000 | 8 |
| 1001 | 9 |
| 1010 | A |
| 1011 | B |
| 1100 | C |
| 1101 | D |
| 1110 | E |
| 1111 | F |
58. Why Hexadecimal is Useful
Binary numbers can become very long.
For example:
1111111010101101
is difficult to read.
Hexadecimal represents every group of four binary bits with one hexadecimal digit:
1111 1110 1010 1101
F E A D
Therefore:
1111111010101101₂ = FEAD₁₆
Hexadecimal is therefore a compact way of representing binary information.
59. Encoding Schemes
Computers internally work with binary data, but humans use characters such as:
A B C 1 2 3 @ # ₹
An encoding scheme defines how characters are represented using numerical/binary values.
Important schemes in the syllabus are:
ASCII
ISCII
Unicode
UTF-8
UTF-32
60. ASCII
ASCII = American Standard Code for Information Interchange
ASCII is a character encoding standard used to represent common English letters, digits, punctuation marks and control characters.
The original ASCII uses 7 bits, allowing:
2⁷ = 128 different codes
Examples
A → 65
B → 66
a → 97
0 → 48
Important Point
ASCII is mainly designed for a relatively limited set of characters and does not by itself cover the writing systems of the world's languages.
61. ISCII
ISCII = Indian Script Code for Information Interchange
ISCII was developed to represent text in several Indian scripts.
It was designed for Indian-language computing before Unicode became widely adopted.
Important Point
ISCII is associated with Indian scripts such as:
Devanagari
Bengali
Gujarati
Gurmukhi
Kannada
Malayalam
Odia
Tamil
Telugu
62. Unicode
Unicode is a universal character set designed to represent characters from many writing systems of the world.
It supports:
English
Hindi
Bengali
Tamil
Telugu
Arabic
Chinese
Japanese
Many other scripts and symbols
Why Unicode is Needed
Imagine a document containing:
Hello
नमस्ते
தமிழ்
বাংলা
A single international character system is needed to represent these characters consistently.
Unicode provides that common framework.
63. UTF-8
UTF-8 = Unicode Transformation Format – 8-bit
UTF-8 is a Unicode encoding that uses a variable number of bytes for characters.
It uses:
1 byte for many basic Latin characters
More bytes for many other Unicode characters
Important Features
Variable-length encoding
ASCII-compatible
Widely used on the Web
Can represent the full Unicode repertoire
Example Concept
Unicode Character
↓
UTF-8
↓
One or more bytes
64. UTF-32
UTF-32 is a Unicode encoding that uses 32 bits (4 bytes) for each Unicode code point.
Features
Fixed-width encoding
Each code point uses 4 bytes
Simple direct representation
Uses considerably more storage than UTF-8 for many common texts
UTF-8 vs UTF-32
| UTF-8 | UTF-32 |
|---|---|
| Variable-length | Fixed-width |
| 1–4 bytes per Unicode code point | 4 bytes per code point |
| Usually more storage-efficient for common text | Usually requires more storage |
| Widely used on the Web | Used in situations where fixed-width representation is useful |
65. ASCII vs Unicode
| ASCII | Unicode |
|---|---|
| Limited character set | Very large universal character repertoire |
| Original ASCII uses 7 bits | Unicode supports characters from many writing systems |
| Mainly designed around English text | Supports global languages/scripts |
| 128 original codes | Much larger repertoire |
Easy Rule
ASCII is limited; Unicode is designed for worldwide text.
66. ISCII vs Unicode
| ISCII | Unicode |
|---|---|
| Designed mainly for Indian scripts | Designed for scripts worldwide |
| Older Indian-language encoding standard | Modern universal character system |
| Limited compared with Unicode | Supports a very large range of scripts |
| Historically important in Indian-language computing | Widely used today |
67. Important Encoding Terms
Character
A symbol such as:
A
7
@
न
Character Set
A collection of characters that can be represented.
Encoding
A method of representing characters as numerical/binary data.
Code Point
A numerical value assigned to a Unicode character.
68. Complete Unit Concept Map
COMPUTER SYSTEMS
│
┌──────────────┼───────────────┐
↓ ↓ ↓
HARDWARE SOFTWARE DATA
│ │ │
┌───┴───┐ ┌───┴────┐ Encoding
↓ ↓ ↓ ↓
Input Output System Application
│ │
│ ┌──┴────────────┐
│ ↓ ↓ ↓
│ OS Utilities Drivers
│
└────────── CPU
│
┌────────┼────────┐
↓ ↓ ↓
ALU CU Registers
│
Memory
│
┌─────────┴─────────┐
↓ ↓
Primary Secondary
│
Cache/RAM
69. Number System Quick Chart
NUMBER SYSTEMS
│
┌─────────────┼──────────────┐
↓ ↓ ↓
Binary Octal Decimal
Base 2 Base 8 Base 10
│
└──────────────┐
↓
Hexadecimal
Base 16
Digit Sets
Binary → 0,1
Octal → 0–7
Decimal → 0–9
Hexadecimal → 0–9, A–F
70. Conversion Method – Master Chart
| Conversion | Main Method |
|---|---|
| Binary → Decimal | Positional weights of 2 |
| Octal → Decimal | Positional weights of 8 |
| Hexadecimal → Decimal | Positional weights of 16 |
| Decimal → Binary | Repeated division by 2 |
| Decimal → Octal | Repeated division by 8 |
| Decimal → Hexadecimal | Repeated division by 16 |
| Binary → Octal | Group 3 bits |
| Binary → Hexadecimal | Group 4 bits |
71. Important Exam Definitions
Computer
An electronic programmable device that accepts input, processes data, stores information and produces output.
Hardware
The physical components of a computer system.
Software
Programs and instructions that tell a computer how to perform tasks.
CPU
The main processing unit that executes instructions and performs processing.
RAM
A volatile read/write primary memory used to hold currently active programs and data.
Cache
Small, high-speed memory used to provide faster access to frequently needed data and instructions.
Operating System
System software that manages hardware/resources and provides services and an interface for users and applications.
Compiler
A translator that converts a high-level program into lower-level/object or machine-oriented code before execution in a compiled toolchain.
Interpreter
A program that translates and executes source instructions progressively during program execution.
Boolean Logic
A logical system based mainly on two values, 0 and 1.
Number System
A method of representing numbers using a defined base and symbols.
ASCII
A character encoding standard whose original form uses 7 bits and defines 128 codes.
Unicode
A universal character set designed to represent text from many writing systems.
72. Important Differences for Examination
RAM vs ROM
| RAM | ROM |
|---|---|
| Generally volatile | Non-volatile |
| Read/write | Primarily used for persistent firmware/instructions |
| Used for active programs/data | Used for information that should persist without power |
| Contents normally lost when power is removed | Contents retained without power |
Cache vs RAM
| Cache | RAM |
|---|---|
| Faster | Slower than cache |
| Smaller | Larger |
| Very close to CPU in memory hierarchy | Main working memory |
| Stores frequently needed data/instructions | Stores active programs and data |
Compiler vs Interpreter
| Compiler | Interpreter |
|---|---|
| Translation generally happens before execution | Translation/execution occurs progressively |
| Often produces object/executable output | Usually executes from source/intermediate representation |
| Compilation errors are generally identified during compilation | Errors may appear when execution reaches the relevant statement/path |
| Compiled execution can be efficient | Interpretation can introduce execution overhead |
System Software vs Application Software
| System Software | Application Software |
|---|---|
| Manages computer resources | Performs user-oriented tasks |
| Provides platform/services for applications | Runs using system software |
| OS is an example | Word processor is an example |
73. Important Questions for Examination
Very Short Answer Questions
What is a computer?
Define hardware.
Define software.
What is CPU?
What is ALU?
What is CU?
What is RAM?
What is cache memory?
What is secondary memory?
What is an operating system?
What is a device driver?
What is a compiler?
What is an interpreter?
What is Boolean logic?
What is ASCII?
What is Unicode?
What is ISCII?
What is UTF-8?
What is UTF-32?
What is the base of hexadecimal number system?
74. Short Answer Questions
Q1. Differentiate between hardware and software.
Answer: Hardware consists of physical components that can be touched, while software consists of programs and instructions used to operate the computer and perform tasks.
Q2. What are the main functions of an operating system?
Answer: Important functions include process management, memory management, file management, device management, security, resource management and providing a user interface.
Q3. What is cache memory? Why is it useful?
Answer: Cache is a small, high-speed memory used to store frequently needed data and instructions so that the CPU can access them faster.
Q4. Differentiate between GUI and CLI.
Answer: GUI allows users to interact using graphical elements such as windows and icons. CLI requires users to type commands.
Q5. What is an assembler?
Answer: An assembler translates assembly language instructions into machine code.
75. Number System Practice Questions
Q1. Convert 10101₂ into decimal.
1×2⁴ + 0×2³ + 1×2² + 0×2¹ + 1×2⁰
= 16 + 0 + 4 + 0 + 1
= 21
Answer: 21₁₀
Q2. Convert 25₁₀ into binary.
25 ÷ 2 = 12 R1
12 ÷ 2 = 6 R0
6 ÷ 2 = 3 R0
3 ÷ 2 = 1 R1
1 ÷ 2 = 0 R1
Read bottom to top:
11001₂
Therefore:
25₁₀ = 11001₂
Q3. Convert 57₈ into decimal.
5×8¹ + 7×8⁰
= 40 + 7
= 47
Answer: 47₁₀
Q4. Convert 3C₁₆ into decimal.
3×16¹ + C×16⁰
= 3×16 + 12
= 48 + 12
= 60
Answer: 60₁₀
Q5. Convert 11110010₂ into hexadecimal.
Group into four:
1111 0010
F 2
Answer: F2₁₆
76. Boolean Logic Practice
Q1. What is the output of AND for inputs 1 and 0?
Answer: 0
Q2. What is the output of OR for inputs 1 and 0?
Answer: 1
Q3. What is the output of XOR for inputs 1 and 0?
Answer: 1
Q4. What is the output of NAND for inputs 1 and 1?
Answer: 0
Q5. What is the output of NOR for inputs 0 and 0?
Answer: 1
Q6. What is NOT 1?
Answer: 0
77. MCQs
1. Which unit is used to represent a single binary digit?
A. Byte
B. Bit
C. KB
D. MB
Answer: B. Bit
2. Which component performs arithmetic and logical operations?
A. CU
B. ALU
C. RAM
D. ROM
Answer: B. ALU
3. Which memory is volatile?
A. RAM
B. ROM
C. SSD
D. DVD
Answer: A. RAM
4. Which is system software?
A. Calculator application
B. Operating system
C. Presentation software
D. Photo editor
Answer: B. Operating system
5. Which translator converts assembly language into machine code?
A. Compiler
B. Interpreter
C. Assembler
D. Browser
Answer: C. Assembler
6. Which gate produces 1 only when both inputs are 1?
A. OR
B. AND
C. XOR
D. NOR
Answer: B. AND
7. Which gate produces 1 when the inputs are different?
A. AND
B. OR
C. XOR
D. NOR
Answer: C. XOR
8. What is the base of binary?
A. 2
B. 8
C. 10
D. 16
Answer: A. 2
9. What is the base of hexadecimal?
A. 2
B. 8
C. 10
D. 16
Answer: D. 16
10. Which encoding is designed to support text from many writing systems?
A. ASCII
B. Unicode
C. Binary
D. Octal
Answer: B. Unicode
11. Which encoding is widely used on the Web?
A. UTF-8
B. UTF-32 only
C. ISCII only
D. BCD
Answer: A. UTF-8
12. ISCII is associated primarily with:
A. Indian scripts
B. Network protocols
C. Operating systems
D. Number systems
Answer: A. Indian scripts
78. Fill in the Blanks
The physical components of a computer are called hardware.
Programs and instructions are called software.
CPU stands for Central Processing Unit.
ALU stands for Arithmetic Logic Unit.
RAM is generally a volatile memory.
The binary number system has base 2.
The octal number system has base 8.
The decimal number system has base 10.
The hexadecimal number system has base 16.
ASCII originally uses 7 bits.
Unicode is designed to represent characters from many writing systems.
UTF-8 is a variable-length Unicode encoding.
UTF-32 uses 4 bytes per Unicode code point.
A program that translates assembly language is called an assembler.
An operating system is system software.
79. True or False
RAM is generally volatile.
TrueA keyboard is an output device.
FalseALU performs arithmetic and logical operations.
TrueAn operating system is application software.
FalseAn assembler translates assembly language.
TrueXOR produces 1 when both inputs are the same.
FalseBinary has base 2.
TrueHexadecimal uses A–F in addition to 0–9.
TrueASCII originally provides 256 codes.
FalseUnicode is designed for multilingual text.
True
80. Match the Following
| Column A | Column B |
|---|---|
| 1. ALU | a. Indian script encoding |
| 2. RAM | b. Arithmetic and logic |
| 3. Assembler | c. Volatile memory |
| 4. ISCII | d. Assembly language translator |
| 5. Unicode | e. Universal character repertoire |
Answers
1 – b
2 – c
3 – d
4 – a
5 – e
81. Quick Revision – One Page
COMPUTER SYSTEM
│
├── Hardware
│ ├── Input
│ ├── Output
│ ├── CPU
│ └── Memory
│
├── Software
│ ├── System Software
│ │ ├── Operating System
│ │ ├── Utilities
│ │ └── Device Drivers
│ │
│ ├── Programming Tools
│ │ ├── Assembler
│ │ ├── Compiler
│ │ └── Interpreter
│ │
│ └── Application Software
│
├── Boolean Logic
│ ├── NOT
│ ├── AND
│ ├── OR
│ ├── NAND
│ ├── NOR
│ └── XOR
│
├── Number Systems
│ ├── Binary → 2
│ ├── Octal → 8
│ ├── Decimal → 10
│ └── Hexadecimal → 16
│
└── Encoding
├── ASCII
├── ISCII
└── Unicode
├── UTF-8
└── UTF-32
82. Golden Rules to Remember
Computer Organisation
Input → Processing → Output → Storage
CPU
CPU = ALU + CU + Registers
Memory
Registers → Cache → RAM → Secondary Storage
Software
System Software → Programming Tools/Translators → Application Software
Translators
Assembly Language → Assembler
High-Level Language → Compiler/Interpreter
Boolean
AND → All 1
OR → Any 1
XOR → Different
NAND → NOT AND
NOR → NOT OR
NOT → Opposite
Number Systems
Binary → 2
Octal → 8
Decimal → 10
Hexadecimal → 16
Encoding
ASCII → Basic character encoding
ISCII → Indian scripts
Unicode → Worldwide character repertoire
UTF-8 → Variable length
UTF-32 → 4 bytes per Unicode code point
83. Final Exam Tips
Learn all important definitions precisely.
Memorise the truth tables of all six gates.
Practise De Morgan's laws.
Practise number-system conversions step by step.
Remember the bases of all four number systems.
Learn the difference between compiler and interpreter.
Understand RAM, ROM, cache and secondary storage.
Remember the functions of an operating system.
Learn ASCII, ISCII, Unicode, UTF-8 and UTF-32 differences.
In numerical questions, always write the base/subscript where required.
Most Important Topics for Revision
⭐ Computer organisation and CPU
⭐ Primary, cache and secondary memory
⭐ Units of memory
⭐ Types of software
⭐ OS functions and interfaces
⭐ All Boolean gates and truth tables
⭐ De Morgan's laws
⭐ Number-system conversions
⭐ ASCII, ISCII and Unicode
⭐ UTF-8 and UTF-32
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