How a Computer Works (2015)

17. Monitor

The Monitor provides a means for displaying activity on the Windows desktop. Computer monitors come in different sizes. A 22 inch monitor is a common size; with a larger monitor the screen is clearer which reduces eyestrain. Two main technologies are used in monitors.

The LED or the liquid crystal display (LCD). The LCD monitor takes up less desk space. Here we will describe how a LCD monitor works.

Pixel

The screens surface contains pixels, the smallest area that can be controlled. Each pixel displays a colour. The pixel element is so small that it is difficult to see on its own.

On a monitors surface thousands of pixels are on the surface in rows and columns, the very narrow gap between them enables an image to be built up.

Display Adapter

Data transfer to Memory (VRAM)

Before the monitor can display an image it receives information from the display adapter in the computer. The display adapter contains VRAM memory, which stores a colour number for each on-screen pixel.

The CPU updates the VRAM memory every time it wishes to change the colour of a pixel. It places a colour number for the pixel it wishes to change in the display adapters VRAM. Each VRAM memory location represents one pixel on the screen.

GMCH

Data bits are sent from the CPU to the Graphics and Memory Controller Hub (GMCH) chip. The controller then routes the data to the AGP universal connector. Data is placed in the display adapters VRAM.

VRAM

Data transfer to Memory (VRAM)

The Display adapter then reads all the VRAM address locations into a special chip which contains three digital to analogue converters one for each of the primary colours used red, green and blue.

The DAC uses a look up table to interpret the digital value to voltage that represents a specific colour. The on board VRAM on the display adapter determines how many colours can be displayed.

Super VGA

Super VGA adapters have enough VRAM to store 16 bits for each colour. This means 16,000 separate colours can be displayed.

With 24 bits a pixel can display up to 16,777,216 different colour shades (True colour).

Resolution

The resolution is the number of pixels that can be displayed horizontally and vertically on the screens surface. These signals also set the monitors refresh rate, which is how frequently the screens image is redrawn.