Computer monitor, coloured X-ray. This type of computer screen is also known as a VDU (visual display unit). It is a CRT (cathode ray tube), which uses the same technology as that used in colour televisions. The electronic circuits (white, lower centre) and a plastic support stand (purple, bottom centre) are seen. The circular structure at centre (green) is the CRT that fires electrons onto the back of a phosphor coated screen, which forms the image.