In number system modern method of representing numbers symbolically is based on positional notations.

In this method, each number is represented by a string of symbols where each symbol is associated with a specific weight depending upon its positions. The total number of different symbols which are used in a particular number system is called the base or radix of the system and the weight of each position of a particular number is expressed as a power of the base. When a number is formed with the combination of the symbols, each symbol is then called a digit and the position of each symbol is referred to as the digit position.

Thus if a number system has symbols starting from 0, and the digits of the system are 0, 1, 2, ….. (r – 1) then the base or radix is r. If a number D of this system be represented by

D = d₀ d₀ ……. d₀…….. d₁ d

then the magnitude of this number is given by

|D| = d_{n-1} r^{n-1} + d_{n-2} r^{n-2} + …… d_{i} r^{i} + …… d_{1} r^{1} + d_{0} r^{0}

Where each d₀ ranges from 0 to r – 1, such that

0 ≤ d₀ ≤ r – 1, i = 0, 1, 2 …… (n – 1).

The digit at the extreme left has the highest positional value and is generally called the **Most Significant Digit**, or in short **MSD**; similarly, the digit occupying the extreme right position has the least positional value and is referred to as the **Least Significant Digit** or **LSD**.