Definition
A character set is a mapping between characters and their numeric codes. It defines which numbers represent which characters.
ASCII
Key Point
ASCII (American Standard Code for Information Interchange):
• 7 bits = 128 characters
• Covers English letters, digits, punctuation, control characters
• 'A' = 65, 'a' = 97, '0' = 48
• Limited - only English characters
• 7 bits = 128 characters
• Covers English letters, digits, punctuation, control characters
• 'A' = 65, 'a' = 97, '0' = 48
• Limited - only English characters
Unicode
Key Point
Unicode:
• Supports over 140,000 characters
• Covers virtually all world languages
• Includes emojis, mathematical symbols, historic scripts
• UTF-8: Variable length (1-4 bytes per character)
• Backward compatible with ASCII
• Supports over 140,000 characters
• Covers virtually all world languages
• Includes emojis, mathematical symbols, historic scripts
• UTF-8: Variable length (1-4 bytes per character)
• Backward compatible with ASCII
Key Point
| Character set | Bits | Characters | Scope |
|---|---|---|---|
| ASCII | 7 | 128 | English only |
| Extended ASCII | 8 | 256 | English + European |
| Unicode (UTF-8) | 8-32 | 140,000+ | All languages + emoji |
Exam Tip
Why Unicode over ASCII?
• Global internet requires all languages
• ASCII cannot represent Chinese, Arabic, Hindi, etc.
• Emojis need Unicode
• UTF-8 is efficient - uses 1 byte for ASCII characters
• Global internet requires all languages
• ASCII cannot represent Chinese, Arabic, Hindi, etc.
• Emojis need Unicode
• UTF-8 is efficient - uses 1 byte for ASCII characters