Cambridge IGCSE Computer Science (0478) · lesson 5 of 35 · 20 min
Why Do We Need Character Sets?
Computers store everything as numbers. To store text, we need an agreed mapping between numbers and characters — a character set. Without a standard, a file created on one computer would display as gibberish on another.
ASCII
ASCII (American Standard Code for Information Interchange) was developed in the 1960s. It uses 7 bits to represent 128 characters (0–127), including:
- Control characters (0–31): newline, tab, carriage return, etc.
- Printable characters (32–126): space, digits 0–9, uppercase A–Z, lowercase a–z, punctuation.
- Character
- Denary
- Binary
- Hex
- A
- 65
- 01000001
- 41
- B
- 66
- 01000010
- 42
- a
- 97
- 01100001
- 61
- 0
- 48
- 00110000
- 30
- Space
- 32
- 00100000
- 20
Key pattern: Uppercase letters start at 65; lowercase at 97. The difference is always 32 (bit 5). Digits start at 48.
Unicode
ASCII only covers English characters. Unicode is an international standard that assigns a unique code point to every character in every language — over 140,000 characters including emoji.
UTF-8 is the most common Unicode encoding. It uses 1 byte for ASCII characters and up to 4 bytes for others, making it efficient for English text while supporting all languages.
What is the ASCII code for the letter “A”?
- 41
- 65
- 97
- 64
Answer: 65
A = 65 in denary (41 in hex).
How many characters does standard ASCII represent?
- 256
- 128
- 512
- 64
Answer: 128
7 bits = 2⁷ = 128 characters.
Which encoding supports all world languages and is backward compatible with ASCII?
- ASCII-256
- UTF-8
- EBCDIC
- ISO-8859
Answer: UTF-8
UTF-8 is the dominant Unicode encoding and is backward compatible with ASCII.
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