A computer display (also known as a computer monitor, computer screen, or computer video display) is a device that can display signals generated by a computer as images on a screen. (From the Latin verb moneo: to warn, or advise.) There are many types of monitors, but they generally conform to display standards. Once an essential component of computer terminals, computer displays have long since become standardized peripherals in their own right.
As with television, several different hardware technologies exist for displaying computer-generated output:
* Liquid crystal display (LCD). (LCD-based monitors can receive television and computer protocols (SVGA, PAL, SECAM; NTSC)). As of this writing (June 2006), LCD displays are the most popular display device for new computers in North America.
* Cathode ray tube (CRT)
o Vector displays, as used on the Vectrex, many scientific and radar applications, and several early arcade machines (notably Asteroids (game) - always implemented using CRT displays due to requirement for a deflection system, though can be emulated on any raster-based display.
o Television receivers were used by most early personal and home computers, connecting composite video to the television set through the use of a modulator. Image quality was reduced by the additional steps of composite video > modulator > TV tuner > composite video, though it reduced costs of adoption by removing the costs of a specialized monitor from the system's price tag. During the era of these early home computers, television sets were almost exclusively CRT-based.
* 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.
The relevant performance measurements of a monitor are:
* Dot pitch. In general, the lower the dot pitch (e.g. 0.24), the sharper the picture will appear.
* Color temperature
* Contrast ratio
* Interface (DVI or VGA, commonly)
* H-sync rate
* V-sync rate
* Response time
* Refresh rate
A modern CRT display has considerable flexibility: it can usually handle a range of resolutions from 320 by 200 pixels (320×200) up to 2048 by 1536 pixels (2048×1536) or 2304 by 1440 pixels (2304×1440), with unlimited colors and a variety of refresh rates. As of 2005, the highest known maximum native resolution for any type of monitor is 3840 by 2400 pixels (3840×2400) on an LCD screen.
Issues and problems
Screen burn-in has been an issue for a long time with CRT computer monitors and televisions. Commonly, people use screensavers in order to prevent their computer monitors from getting screen burn-in. How this happens is that if an image is displayed on the screen for a long period of time without changing, the screen that is showing will embed itself into the glass. Generally, you will find this phenenomon at older ATM machines. In order to prevent screen burn-in on computer monitors, it is recommended that you use a good screensaver program that rotates often.
The other issue with computer monitors is that some LCD monitors may get "dead pixels" over time. This generally applies to older LCD monitors from the 1990's.
Things on both issues have changed over time and are improving in order to prevent these things from happening.
With exceptions of DLP, most display technologies (especially LCD) have an inherent misregistration of the color planes, that is, the centers of the red, green, and blue dots do not line up perfectly. Subpixel rendering depends on this misalignment; technologies making use of this include the Apple II from 1976, and more recently Microsoft (ClearType, 1998) and XFree86 (X Rendering Extension).
Configuration and usage
Some users use more than one monitor. The displays can operate in multiple modes. One of the most common spreads the entire desktop over all of the monitors, which thus act as one big desktop. The X Window System refers to this as "Xinerama".
A monitor may also clone another monitor.
* Dualhead - Using two monitors
* Triplehead - using three monitors
* Display assembly - multi-head configurations actively managed as a single unit
The X Window System provides configuration mechanisms for using a single hardware monitor for rendering multiple virtual displays, as controlled (for example) with the Unix DISPLAY global variable or with the -display command option.