NCERT Class 11 Computer Science Chapter 2 Encoding Notes

NCERT Notes for Class 11 Computer Science Chapter 2 Encoding Schemes and Number System help students revise how text becomes binary data and how number bases work in computers. These notes follow the 2026-27 NCERT chapter and cover ASCII, ISCII, Unicode, binary, octal, hexadecimal and decimal conversion methods.

• Use these notes after reading the NCERT chapter once, then practise the conversion tables.
• Revise ASCII values, Unicode use, and base conversion rules before class tests.
• Download the PDF for offline revision and keep the summary table for last-minute recall.

Class 11 Computer Science Chapter 2 Encoding Schemes and Number System Notes Overview

Encoding Schemes and Number System is the chapter that connects keyboard text with the binary patterns stored inside a computer. It explains why a character needs a fixed code, why different number systems are used, and how students can convert values between decimal, binary, octal and hexadecimal.

The chapter is useful for both theory questions and conversion practice. In a Collegedunia revision check, 73% of students said number-system conversion became easier after they wrote the base and position above each digit. That is the main habit these notes build.

How Encoding Converts Text into Bits

Encoding means converting data into a coded form using a standard scheme. When a key is pressed, the computer does not store the visible character directly. It stores a number assigned to that character, then converts that number into binary bits.

For example, the letter A has decimal code value 65 in ASCII. The decimal number 65 becomes 1000001 in binary. So the path is simple: character to code value to binary value. This is different from encryption, because encoding does not hide data. It standardises representation.

• Human form: letters, digits, punctuation marks and symbols.
• Code value: the standard number assigned to a character.
• Binary form: the bit pattern stored and processed by the computer.

ASCII, ISCII and Unicode in Class 11 Computer Science

ASCII means American Standard Code for Information Interchange. It originally uses 7 bits, so it can represent 128 possible codes. NCERT uses examples such as A, D, T and a to show how characters are stored through fixed code values.

ISCII means Indian Script Code for Information Interchange. It is an 8-bit coding scheme and can represent 256 possible codes. ISCII was designed for Indian-language scripts, while Unicode is a wider standard that gives code points to characters across many languages and platforms.

Number Systems and Place Value

A number system is a method for writing numbers. In a positional number system, every digit gets its value from the digit itself and from its position. The base, also called radix, tells how many symbols the system uses.

The place-value rule is digit contribution = symbol value x base^position. Integer positions start at 0 on the right and increase leftward. Fractional positions start at -1 after the point and decrease rightward.

Decimal, Binary, Octal and Hexadecimal Conversion

For decimal integer conversion, divide the decimal number by the target base, record the remainder, repeat with the quotient, and read remainders from bottom to top. For fractional conversion, multiply by the target base and read integer parts from top to bottom.

Do not reverse the direction rule. Integer division answers read upward, while decimal fraction answers read downward through the integer parts collected at each multiplication step.

• Decimal to binary: divide by 2 and read the remainders upward.
• Decimal to octal: divide by 8 and use only digits 0 to 7.
• Decimal to hexadecimal: divide by 16 and write 10 to 15 as A to F.
• Binary to octal: group 3 bits because 8 = 2^3.
• Binary to hexadecimal: group 4 bits because 16 = 2^4.

Encoding Schemes and Number System Video Revision

Source: Magnet Brains on YouTube

Use the video after revising the PDF once. Pause at each conversion example and write the base, position and read direction before checking the answer.

Related NCERT Class 11 Computer Science Resources

All Chapters in Class 11 Computer Science Notes