Curriculum
Grade XI Computer Science
Lessons
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Le-1 Computer System
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Le-2 Encoding Schemes and Number System
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le-3 Emerging Trends
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Le-4 Introduction to Problem Solving
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Le-5 Getting Started with Python
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Le-6 Flow of Control
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Le-7 Functions
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Le-8 Strings
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Le-9 Lists
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Le-10 Tuples and Dictionaries
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Le-11 Societal Impact
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Notes
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Work Sheets
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Le-2 Encoding Schemes and Number System
School Revise · Class 11 Computer Science · Chapter 2
Encoding Schemes and Number System
Code 083, Class 11. Computers store everything as 0s and 1s. Here we meet the number systems used in computing and the schemes that turn letters into numbers a computer can hold.
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What this chapter is about
Inside a computer, every number, letter and symbol is stored as a pattern of bits (0s and 1s). In this chapter we learn the number systems used in computing, how to convert a decimal number to binary, and how characters are encoded.
1. Number systems
A number system has a base, which is how many different digits it uses. Computers work in binary because a circuit is easily off (0) or on (1).
| Number system | Base | Digits used |
| Binary | 2 | 0, 1 |
| Octal | 8 | 0 to 7 |
| Decimal | 10 | 0 to 9 |
| Hexadecimal | 16 | 0 to 9, A to F |
2. Converting decimal to binary
Divide the number by 2 again and again, writing down each remainder, then read the remainders from bottom to top.
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Example: convert 13 to binary. 13/2 gives 6 remainder 1, 6/2 gives 3 remainder 0, 3/2 gives 1 remainder 1, 1/2 gives 0 remainder 1. Reading upwards: 1101. So 13 in decimal is 1101 in binary. |
3. Encoding schemes
An encoding scheme gives each character a number. ASCII uses 7 bits and covers English letters, digits and symbols (for example, A is 65). Unicode is a universal scheme that covers the letters of almost every language. ISCII was made for Indian scripts.
Practise with the interactive
Type a small decimal number and watch it turn into binary step by step, and see the ASCII code of a letter. The interactive opens right here in the lesson.
Practice set A, multiple choice
1. The base of the binary number system is …
2, because it uses only two digits, 0 and 1.
2. How many bits does standard ASCII use?
7 bits, which gives 128 different characters.
3. The decimal value of the binary number 1010 is …
10. The place values are 8, 0, 2, 0, which add to 10.
4. Which scheme covers the letters of almost every language?
Unicode, a universal encoding scheme.
Practice set B, short answer
1. Convert the decimal number 6 to binary.
110. 6/2 gives 3 r0, 3/2 gives 1 r1, 1/2 gives 0 r1, read upwards 110.
2. State one difference between ASCII and Unicode.
ASCII covers mainly English in 7 bits; Unicode is universal and covers almost all languages.
3. Why do computers use the binary system?
A circuit is easily in one of two states, off (0) or on (1), so binary is simple and reliable to store.
Quick summary
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Number systems have a base: binary (2), octal (8), decimal (10) and hexadecimal (16). Decimal converts to binary by repeated division by 2, reading remainders upwards. Encoding schemes give characters numbers: ASCII (7 bits, English), Unicode (universal) and ISCII (Indian scripts). |
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These free Class 11 Computer Science notes explain number systems, binary octal decimal and hexadecimal, decimal to binary conversion, and encoding schemes ASCII Unicode and ISCII, with worked examples and practice, for CBSE students across India and the Gulf including the UAE, Saudi Arabia, Qatar, Oman, Kuwait and Bahrain.
© 2026 School Revise. All rights reserved. Original content aligned to the CBSE and NCERT Class 11 Computer Science syllabus. Unauthorised copying is not permitted.
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