Character Sets – ASCII & Unicode

Character Sets Overview

• Character set: the list of numeric codes recognised by hardware & software to represent characters.
• Each character ⟶ unique character code ⟶ stored as binary.

ASCII

• Original ASCII: $7$-bit; represents $128$ characters (codes $0\text{–}127$).
• Extended ASCII: $8$-bit; represents $256$ characters (codes $0\text{–}255$).
• Content groups
  • Uppercase $A\text{–}Z$: $65\text{–}90$
  • Lowercase $a\text{–}z$: $97\text{–}122$
  • Digits $0\text{–}9$: $48\text{–}57$
  • Control & punctuation occupy remaining ranges.
• Example codes: $A=65=1000001<em>2$, $a=97=1100001</em>2$.
• Codes run in sequence → knowing one code lets you calculate others (e.g. $A+4=E$).

Unicode

• Universal character set; typical form UTF-16 uses $16$ bits → $65{,}536$ possible codes (many modern encodings extend further).
• First $128$ codes identical to ASCII for compatibility.
• Supports scripts beyond Latin: Greek, Mandarin, Japanese, emoji, etc.
• Advantages over ASCII:
  • Vastly larger range of symbols.
  • One standard for multilingual text & modern symbols (e.g. emoji on phones).

Encoding Tables & Code Calculation

• Character codes are grouped and sequential; patterns aid quick conversion:
  • Add $32$ to convert uppercase → lowercase (e.g. $A(65)+32=97(a)$).
  • Digits follow $48$, so digit $n$ has code $48+n$.
• Conversion steps
  1. Denary code → binary (e.g. $71\rightarrow01000111$).
  2. Binary → denary to identify character.

Key Comparisons & Exam Tips

• Bits per character: ASCII $7/8$ vs Unicode $16$ (or $8\text{–}32$ in UTF encodings).
• Capacity: ASCII $128/256$ symbols; Unicode $65{,}536+$.
• Use Unicode whenever multiple languages or emoji are required; ASCII suffices for basic English text.