Monitor

A monitor or display (sometimes called a visual display unit) is a piece of electrical equipment which displays images generated by devices such as computers, without producing a permanent record. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD), while older monitors use a cathode ray tube (CRT).
The size of a display is usually given as the distance between two opposite screen corners. One problem with this method is that it does not distinguish between the aspect ratios of monitors with identical diagonal sizes, despite the fact that the area of a given diagonal span decreases as it becomes less square. For example, a 4:3 21-inch (53.3 cm) monitor has an area of about 211 sq in (1,361 cm²), while a 16:9 21-inch widescreen has about 188 sq in (1,213 cm²).This method of measurement is from the first types of CRT television, when round picture tubes were in common use. Being circular, they only needed to use their diameter to describe their tube size. When round tubes were used to display rectangular images, the diagonal measurement was equivalent to the round tube's diameter. This method continued even when CRT tubes were manufactured as rounded rectangles.