What is a character set?

all the characters a computer can represent, each with a unique code. Each character is matched to its own binary code.

Standard ASCII uses 7 bits for each character. How many different characters can it represent?

128. 2 multiplied by itself seven times is 128.

Why can Unicode represent more characters than ASCII?

It uses more bits for each character. More bits means more possible codes.

The ASCII code for 'A' is 65. What is the code for 'D'?

68. B is 66, C is 67 and D is 68.

What is a drawback of Unicode compared with ASCII?

A character can need more bits, so files can be larger. More bits for each character means more storage.

Text: ASCII and Unicode · Cambridge IGCSE Computer Science

In plain words

A computer cannot store the letter A. It stores a number, and everyone agrees which number means which character. That agreed list is a character set.

When you press a key, the code for that character is what gets stored, in binary.

5 things to know

A character set is all the characters a computer can represent, each with its own unique binary code.
ASCII uses 7 bits for each character, which gives 128 different codes: enough for the English alphabet, digits and common symbols. Extended ASCII uses 8 bits for 256.
Unicode uses more bits for each character, so it has room for far more: the alphabets of many languages, mathematical symbols and emojis.
Because Unicode uses more bits for each character, the same text can take up more storage.
The codes run in order. In ASCII, A is 65, B is 66 and C is 67. Lower-case letters have their own codes: a is 97.

Worked example

The ASCII code for the letter A is 65. Find the 8-bit binary code that stores the letter E.

The codes go up in alphabetical order. E is four letters after A.
65 + 4 = 69.
69 = 64 + 4 + 1, which is 01000101.

Tips and tricks

Compare the two the right way round: Unicode can represent more characters because it uses more bits per character.
The character '7' is not stored as the number 7. Digits typed as text have character codes of their own.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Text: ASCII and Unicode: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is a character set?
- a list of the fonts on a computer
- all the characters a computer can represent, each with a unique code (the answer)
- the keys on a keyboard
- a way of compressing text
Each character is matched to its own binary code.
Standard ASCII uses 7 bits for each character. How many different characters can it represent?
- 7
- 64
- 128 (the answer)
- 256
2 multiplied by itself seven times is 128.
Why can Unicode represent more characters than ASCII?
- It compresses each character.
- It uses more bits for each character. (the answer)
- It stores characters as pictures.
- It only stores capital letters.
More bits means more possible codes.
The ASCII code for 'A' is 65. What is the code for 'D'?
- 66
- 67
- 68 (the answer)
- 69
B is 66, C is 67 and D is 68.
What is a drawback of Unicode compared with ASCII?
- It cannot store English letters.
- A character can need more bits, so files can be larger. (the answer)
- It cannot be used on the internet.
- It has fewer symbols.
More bits for each character means more storage.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

2 questions, 4 marks. Write your answers on paper, then check them.

Text: ASCII and Unicode

Cambridge IGCSE Computer Science 0478 · 4 marks · papermunch.org

Name ______________________________ Date ______________

Explain why Unicode is used as well as ASCII.[2]
Show answerHide answer
ASCII has too few codes for every language. Unicode uses more bits for each character, so it can represent many more characters, including other alphabets and emojis.
I got this one
The ASCII code for 'a' is 97. State the code for 'e' and explain how you worked it out.[2]
Show answerHide answer
101. The codes run in alphabetical order and e is four letters after a.
I got this one

Answers: Text: ASCII and Unicode

1. ASCII has too few codes for every language. Unicode uses more bits for each character, so it can represent many more characters, including other alphabets and emojis.
2. 101. The codes run in alphabetical order and e is four letters after a.