A number can be represented with different base values. We are familiar with the
numbers in the base 10 (known as decimal numbers), with digits taking values
0,1,2,…,8,9.
A computer uses a Binary number system which has a base 2 and digits can have only
TWO values: 0 and 1.
A decimal number with a few digits can be expressed in binary form using a large
number of digits. Thus
the number 65 can be expressed in binary form as 1000001.
The binary form can be expressed more compactly by grouping 3 binary digits together to
form an octal
number. An octal number with base 8 makes use of the EIGHT digits
0,1,2,3,4,5,6 and 7.
A more compact representation is used by Hexadecimal representation which groups 4
binary digits together. It can make use of 16 digits, but since we have only 10 digits, the
remaining 6 digits are made up of first 6 letters of the alphabet. Thus the hexadecimal
base uses 0,1,2,….8,9,A,B,C,D,E,F as digits.
To summarize
Decimal : base 10
Binary : base 2
Octal: base 8
Hexadecimal : base 16