The number system that computers use is binary. Binary is a base-2 system as it only uses two digits, 0 and 1.

A binary digit, or bit, is the smallest unit of data in computing. All data (music, images, software) processed by a computer is stored in bits.

Any data or instructions sent to the CPU must first be changed into binary code, also known as machine code.

The circuits in a computer's processor are made of billions of transistors. Each of these transistors is a switch that reacts to the electronic signals it receives. The bits 0 and 1 correspond with the 'on' and 'off' states of the transistors.

How are numbers and letters represented in binary?

Binary numbers

A number base indicates how many digits are available in a numerical system. The denary (or decimal) system is known as base-10 because there are ten choices of digits between 0 and 9. For binary numbers, there are only two possible digits available (0 or 1), so it is also known as base-2.

In a base-2 system, each place value increases by a power of 2. The first place value is 20 (1), the second is 21 (2), the third is 22 (4), the fourth is 23 (8) and so on. We could represent 8 bits (one byte) of data using the table below.

Consider the binary number 1001 0011:


This binary number represents 128 + 16 + 2 + 1. Or 27 + 24 + 21 + 20.

The sum of these values is 147.

Therefore, the 8-bit binary number 1001 0011 represents 147 in denary.