Visual display unit

A visual display unit, often called simply a monitor, is a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record. The word "monitor" is used in other contexts; in particular in television broadcasting, where a television picture is displayed to a high standard. A computer display device is usually either a cathode ray tube or some form of flat panel such as a TFT LCD. The monitor comprises the display device, circuitry to generate a picture from electronic signals sent by the computer, and an enclosure or case. Within the computer, either as an integral part or a plugged-in interface, there is circuitry to convert internal data to a format compatible with a monitor.

Diagonal size

The inch size is the diagonal size of the picture tube or LCD panel. With 4:3 CRTs the picture is squarer than 16:10 TFT and so has a larger area for the same diagonal, hence a 17" CRT generally gives about the same area of picture as a 19" TFT.

This method of size measurement dates from the early days of CRT television when round picture tubes were in common use, which only had one dimension that described display size. When rectangular tubes were used, the diagonal measurement of these was equivalent to the round tube's diameter, hence this was used.

A better way to compare CRT and LCD displays is by viewable image size.

As with television, several different hardware technologies exist for displaying computer-generated output:

• Liquid crystal display (LCD). TFT LCDs are the most popular display device for new computers in the world.
  • Passive LCD gives poor contrast and slow response, and other image defects. These were used in some laptops until the mid 1990s.
  • TFT Thin Film Transistor LCDs give much better picture quality in several respects. All modern LCD monitors are TFT.
• Cathode ray tube (CRT)
  • Standard raster scan computer monitors
  • Vector displays, as used on the Vectrex, many scientific and radar applications, and several early arcade machines (notably Asteroids) - always implemented using CRT displays due to requirement for a deflection system, though can be emulated on any raster-based display.
  • Television receivers were used by most early personal and home computers, connecting composite video to the television set using a modulator. Image quality was reduced by the additional steps of composite video ? modulator ? TV tuner ? composite video.
• Plasma display
• Surface-conduction electron-emitter display (SED)
• Video projector - implemented using LCD, CRT, or other technologies. Recent consumer-level video projectors are almost exclusively LCD based.
• Organic light-emitting diode (OLED) display
• Penetron military aircraft displays

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