The two most common:

• ASCII (ISO 646)
  • 7-bit values, using lower 7-bits of a byte (top bit always zero)
  • can encode roman alphabet, digits, punctuation, control chars
• UTF-8 (Unicode)
  • 8-bit values, with ability to extend to multi-byte values
  • can encode all human languages plus other symbols

    (e.g.  √   ∑   ∀   ∃   or )