Character Sets: ASCII and Unicode

Character Sets Overview

• A character set is the complete list of binary codes a computer can recognise & process.
• Each character (letter, digit, symbol, control code) is mapped to a unique numeric value that is stored as binary.

ASCII (American Standard Code for Information Interchange)

• Uses $7$ bits per character ⇒ $128$ possible codes $\left(0!\text{–}!127\right)$.
• Key groupings (sequential):
  • Capital letters $A!\text{–}!Z:65\text{–}90$
  • Lowercase $a!\text{–}!z:97\text{–}122$
  • Digits $0!\text{–}!9:48\text{–}57$
• Example mappings:
  • $A=65=1000001<em>2$ • $G=71=01000111</em>2$
  • $*=42=00101010_2$
• Codes are consecutive, so knowing one lets you calculate others (e.g. $E=65+4=69$).
• Limitations: only $128$ characters; no support for accented letters, non-Latin scripts, emoji.

Unicode

• A universal character set covering virtually every written language & symbol.
• Original size: $16$ bits (BMP) ⇒ $65\,536$ codes. Modern UTF encodings scale to over $2\,147\,483\,647$ characters.
• First $128$ codes mirror ASCII for compatibility.
• Supports scripts such as Greek, Mandarin, Japanese, plus emoji & technical symbols.

Advantages of Unicode over ASCII

• Far larger code space; accommodates multilingual text and pictographs.
• Consistent cross-platform standard.
• Essential for devices/apps that handle diverse languages or emoji (e.g., smartphones).

Exam Quick-Recall Points

• Character set = set of binary codes understood by hardware & software.
• ASCII: $7$ bits, $128$ characters; understand control vs printable ranges.
• Unicode: $16$+ bits, millions of characters; required for global language support.
• Character codes are grouped & run in sequence—use this to convert or infer values.
• Practise conversions: denary $\leftrightarrow$ binary for ASCII codes.
• Be ready to justify why Unicode is chosen over ASCII when additional symbols/languages are needed.