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.

Contents [hide] 1 Screen size 1.1 Diagonal size 1.2 Widescreen area 2 Imaging technologies 2.1 Cathode ray tube 3 Performance measurements 3.1 Comparison 3.1.1 CRT 3.1.2 Passive LCD 3.1.3 TFT LCD 3.1.4 Plasma 3.1.5 Penetron 4 Problems 4.1 Dead pixels 4.2 Stuck pixels 4.3 Phosphor burn-in 4.4 Plasma burn-in 4.5 Black level misadjustment 4.6 Glare 4.7 Color misregistration 4.8 Incomplete spectrum 5 Display interfaces 5.1 Computer Terminals 5.2 Composite signal 5.3 Digital monitors 5.3.1 TTL monitors 5.3.2 Single color screens 6 Modern technology 6.1 Analog RGB monitors 6.2 Digital and analog combination 7 Configuration and usage 7.1 Multi-head 7.2 Virtual displays 8 Additional features 8.1 Power saving 8.2 Directional screen 8.3 Touch screen 9 Major manufacturers 10 See also 11 References 12 External links

[edit] Screen size

Main article: Screen size

[edit] 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.

[edit] Widescreen area

A widescreen display always has less screen area for a given quoted inch size than a standard 4:3 display, due to its basic geometry.

[edit] Imaging technologies

19" inch (48.3 cm tube, 45.9 cm viewable) CRT computer monitor

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

[edit] Cathode ray tube

CRT Computer display pixel array(right)

The CRT or cathode ray tube, is the picture tube of a monitor. The back of the tube has a negatively charged cathode. The electron gun shoots electrons down the tube and onto a charged screen. The screen is coated with a pattern of dots that glow when struck by the electron stream. Each cluster of three dots, one of each color, is one pixel.

The image on the monitor screen is usually made up from at least tens of thousands of such tiny dots glowing on command from the computer. The closer together the pixels are, the sharper the image on screen can be. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. Most monitors have a dot pitch of 0.28 mm or less.

There are two electromagnets around the collar of the tube which deflect the electron beam. The beam scans across the top of the monitor from left to right, is then blanked and moved back to the left-hand side slightly below the previous trace (on the next scan line), scans across the second line and so on until the bottom right of the screen is reached. The beam is again blanked, and moved back to the top left to start again. This process draws a complete picture, typically 50 to 100 times a second. The number of times in one second that the electron gun redraws the entire image is called the refresh rate and is measured in hertz (cycles per second). It is common, particularly in lower-priced equipment, to use a technique called interlacing, in which all the odd-numbered lines of an image are traced, and then all the even-numbered lines; the circuitry of such an interlaced display need be capable of only half the speed of a non-interlaced display. An interlaced display, particularly at a relatively low refresh rate, can appear to some observers to flicker, and may cause eyestrain and nausea.