page_title: Computer monitor
section_title: Size
hierarchical_section_title: Computer monitor / Measurements of performance / Size
context_page_description: A computer monitor is an output device that displays information in pictorial form. A monitor usually comprises the visual display, circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display with LED backlighting having replaced cold-cathode fluorescent lamp backlighting. Older monitors used a cathode ray tube. Monitors are connected to the computer via VGA, Digital Visual Interface, HDMI, DisplayPort, Thunderbolt, low-voltage differential signaling or other proprietary connectors and signals.
  Originally, computer monitors were used for data processing while television sets were used for entertainment. From the 1980s onwards, computers have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and computer monitors, has changed from 4:3 to 16:10, to 16:9.
  Modern computer monitors are easily interchangeable with conventional television sets and viceversa.
context_section_description: On two-dimensional display devices such as computer monitors the display size or view able image size is the actual amount of screen space that is available to display a picture, video or working space, without obstruction from the case or other aspects of the unit's design. The main measurements for display devices are: width, height, total area and the diagonal.
  The size of a display is usually by monitor manufacturers given by the diagonal, i.e. the distance between two opposite screen corners. This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, it was the external diameter of the glass envelope that described their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangular image was smaller than the diameter of the tube's face (due to the thickness of the glass). This method continued even when cathode ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size, and was not confusing when the aspect ratio was universally 4:3.
  With the introduction of flat panel technology, the diagonal measurement became the actual diagonal of the visible display.  This meant that an eighteen-inch LCD had a larger visible area than an eighteen-inch cathode ray tube.
  The estimation of the monitor size by the distance between opposite corners does not take into account the display aspect ratio, so that for example a 16:9 21-inch (53 cm) widescreen display has less area, than a 21-inch (53 cm) 4:3 screen. The 4:3 screen has dimensions of 16.8 in × 12.6 in (43 cm × 32 cm) and area 211 sq in (1,360 cm²), while the widescreen is 18.3 in × 10.3 in (46 cm × 26 cm), 188 sq in (1,210 cm²).
caption: The area, height and width of displays with identical diagonal measurements vary dependent on aspect ratio.
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