An Analogue signal is made up of continuous electrical signals or waves, while a digital signal uses pulses equivalent to the binary digits 0 and 1.

Most CRT and some LCD monitors require the signal information in analogue form and not digital , they typically use an analogue connection. However, computers work in a digital world. The computer and video adapter convert digital data into analogue format. A video adapter is an expansion card or component that provides the ability to convert display information into a signal that is sent to the monitor. It can also be called a graphics adapter, video card or graphics card.

Once the display information is in analogue form, it is sent to the monitor through a VGA cable. The cable connects at the back of the computer to an analogue connector (also known as a D-Sub connector) that has 15 pins in three rows.

A VGA connector has three separate lines for the red, green and blue colour signals, and two lines for horizontal and vertical sync signals. In a normal television, all of these signals are combined into a single composite video signal. The separation of the signals is one reason why a computer monitor can have so many more pixels than a TV set.

Other analogue cables used around the globe are: S-Video, Composite, Component and Coaxial.