Denary (Base 10)
Standard number system using digits 0-9. Each place value is a power of 10.
Binary (Base 2)
Used by computers (logic gates). 0 or 1 only. Place values: 128, 64, 32, 16, 8, 4, 2, 1.
Hexadecimal (Base 16)
Shortens binary. Digits 0-9 then A(10) to F(15). One hex digit = 4 bits (a nibble).