Computer display

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Image:Monitor.arp.750pix.jpg A computer display, monitor or screen is a computer peripheral device capable of showing characters and/or still or moving images generated by a computer and processed by a graphics card. Monitors generally conform to one or more display standards. Sometimes the name "display" suits better than the word "monitor", as the latter term can also ambiguously refer to a "machine-level debugger" or to a "thread synchronization mechanism". Some people also refer to computer displays as "heads", especially when talking about multiple displays connected to a single physical computer. Once an essential component of a computer terminal, computer displays have long since become standardized peripherals in their own right.

1 Hardware
2 Configuration and usage
- 2.1 Multi-head
- 2.2 Virtual displays
3 See also
4 External links

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Hardware

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Technologies

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

Cathode ray tube (CRT)
Liquid crystal display (LCD). [LCD-based monitors can receive television and computer protocols (SVGA, PAL, SECAM; NTSC).)
Plasma display (rarely seen)
Video projector

A modern CRT display has considerable flexibility: it can often handle a range of resolutions from 640 by 480 pixels (640×480) up to 2048 by 1536 pixels (2048×1536), with 32-bit colour and a variety of refresh rates.

Dot pitch measures the sharpness of a display. In general, the lower the dot pitch, (e.g. .24), the sharper the picture will appear.

Early CRT-based VDUs (Visual Display Units) without graphics capabilities gained the label "glass teletypes", because of the functional similarity to their electromechanical predecessors.

Black-and-white displays can only display one colour: either as on or off. Monochrome displays can show only levels of a single colour. In both cases the display usually uses green, orange (amber) or gray (white).

Image:Monitor.jpg Colour monitors may show either digital colour (turning each of the red, green and blue signals either on or off, giving eight possible colours: black, white, red, green, blue, cyan, magenta and yellow) or analog colour (red, green and blue signals vary continuously, allowing the display of any combination). Digital monitors are sometimes known as TTLs because the voltages on the red, green and blue inputs are compatible with TTL logic chips.

Most modern computer displays can show thousands or millions of different colours in the RGB colour space by combining red, green, and blue dots in varying intensities.

Some display technologies (especially LCD) have an inherent misregistration of the colour 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 [1], and more recently Microsoft (ClearType, 1998) and XFree86 (X Rendering Extension).

Moving texts can appear in italics, even when the display resolution is too low to show static italics: a fractional time delay causes an apparent corresponding shift of a fraction of a pixel.

Note the sometimes disputed issue of screen emissions.

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History

A trend of miniaturisation within computer displays has seen a general move away from the older, bulky CRT devices in the general direction of flat screens as found in modern laptops.

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Major manufacturers

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Configuration and usage

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Multi-head

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}} 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.

Terminology:

dualhead - Using two monitors
triplehead - using three monitors
display assembly - multi-head configurations actively managed as a single unit

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Virtual displays

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.

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