📚 Knowledge Library — Topic 1 — Data Representation

Text Representation

Learn how computers store letters, numbers, symbols and emoji using character sets, ASCII, Unicode and binary codes.

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1. Invitation

Computers do not store letters.

When you type the letter A, the computer does not store the shape of the letter.

It stores a number. That number is then represented in binary.

💡 Remember: text becomes numbers first, then those numbers become binary.
Figure 1.1
Text becomes binary
A
↓
65
↓
01000001
2. Big Idea

A character set is a codebook.

A character set maps each character to a unique code. Characters include letters, digits, punctuation marks and symbols.

The computer uses this mapping to convert text into binary and binary back into text.

Character set mapping

Character
Denary code
Binary code
A
65
01000001
Figure 2.1
The codebook idea
Character Set
↓
A = 65
B = 66
C = 67
3. Bridge

Think of every character having a locker number.

In a school, every student can have a unique locker number. The locker number identifies one student.

A character set works in a similar way. Each character has its own unique number so the computer knows exactly which character is meant.

💡 Bridge: the computer does not remember the drawing of A. It remembers the code for A.
Figure 3.1
Unique codes
A → 65
B → 66
C → 67

No duplicates
4. ASCII

ASCII is an early character set.

Standard ASCII uses 7 bits. This gives 128 possible character codes.

ASCII can represent basic English letters, digits, punctuation and control characters, but it is limited for world languages and modern symbols.

ASCII example

01000001₂ = 65₁₀
ASCII code 65 = A
🎯 Exam Tip: standard ASCII uses 7 bits, although it is often stored using 8 bits.
Figure 4.1
ASCII sequence
A = 01000001
B = 01000010
C = 01000011
Each letter increases by 1.
5. Unicode

Unicode was developed for the whole world.

ASCII does not have enough codes for all languages, scripts, symbols and emoji.

Unicode was developed to represent a much larger range of characters from around the world.

🎯 Exam Tip: when asked why Unicode was developed, mention more characters and support for international languages.
Figure 5.1
ASCII vs Unicode
ASCII
128 characters

→

Unicode
many more characters
6. Worked Example

Converting ASCII binary to denary.

To convert an ASCII binary value to denary, use the binary place values and add the columns that contain 1.

Convert 00110001₂ to denary

32
16
1
1
1
1
32 + 16 + 1 = 49
ASCII denary 49 represents the character "1".
Figure 6.1
Binary to Denary
00110001
↓
32 + 16 + 1
↓
49
7. Exam Tip

Use precise wording.

In exam answers, do not just write that each character “has a binary value”.

Say that each character is assigned a unique binary value by a character set.

🎯 Exam Tip: the word unique matters. It shows that each character has its own separate code.
Figure 7.1
Precise answer
Character set
↓
unique binary value
↓
stored in sequence
8. Common Mistake

Do not describe the keyboard.

Students sometimes answer text representation questions by describing how a keyboard works.

The question is usually asking how text is stored, so focus on character sets, unique codes and binary representation.

⚠️ Common Mistake: “The user presses a key” is not enough. Explain how the character is represented in binary.
Figure 8.1
Answer the right question
Not keyboard operation

✓

Character set mapping
9. Summary

What you should now know.

A character set maps characters to unique binary values.

ASCII is limited. Unicode supports many more characters and languages, but may require more storage.

Computers store text in binary because electronic circuits use two states: on and off.

Figure 9.1
Text Representation Summary
Character Set
ASCII
Unicode
Unique Codes
Binary Storage