Numbers and their storage in computers.

Base or Radix numbers (positional)
  One's column, 10's column, 100's column, etc.

Some base numbering systems.
  Decimal : Base 10 - range of digits 0-9 (Hindu-Arabic)

  Vigesimal : Base 20 - Aztec, Mayan, Ainu(East Asian), Santali (India), 
    Basque(Europe), and others.

  Sexagesimal : Base 60 - used for time and polar coordinates (our earth).

  Binary :  Base 2,  0-1 - very compatible with digital electronics.
     Altair 8800

  Octal  :  Base 8, 0-7 - 3 bit grouping.

  Hexadecimal : Base 16, 0-9A-F - 4 bit grouping.


Computer Numbers
  Early systems used BCD  4 bit (nibble) storage.
    + Easy to debug data

    + More easily mapped to readable i/o.

    - Inefficiently uses memory

    - Numeric functions more complicated when handling carries.

    Many CPUs still support BCD mode math.

  Binary
    All bits in byte or word used.
    
    Standardized on grouping of 8 bits. 8, 16, 32, 64, 128
 
    Easily represented by octal or hexadecimal representation.
 
    Behaves similar to decimal in real world using simple carry.

    Numeric functions often native to digital logic.