CoMPuTeR DisPLaY

An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the system to the outside.



• COMPUTER DISPLAYS
Computer displays is also called a displays screen or video display terminal (VDT). Monitor
Is screen used to displays the output of computer. Images are represented on monitor by individual dots called pixels. Pixels are the smallest unit on the screen that can be turned on and off or made different shades. The density of the dots determines the clarity of the images and the resolution.


• INTERLACED AND NON-INTERLACED
An inter technique refreshes the lines of the screen by exposing all odd lines first then all even lines next. A non-interlaced technology that is developed later refreshes all the lines on the screen from the top to bottom. The non-interlaced method gives more stable video displays than interlaces method. Two form of displays cathode-ray tube and flat-panel



• Cathode Ray Tubes (CRT)
Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a tube. To release electrons into the tube, they first must be detached from the atoms of the cathode. In early vacuum tubes (Crookes tubes) this was done solely by the high electrical potential between the anode and the cathode. In modern tubes this is assisted by making the cathode a thin wire filament and passing an electric current through it. The current heats the filament red hot. The increased random heat motion of the filament atoms knocks electrons out of the atoms at the surface of the filament, into the evacuated space of the tube. This process is called thermionic emission.



• Monochrome monitor
Monochrome monitor is a type of computer display which was very common in the early days of computing, from the 1960s through the 1980s, before the colour monitors became popular. They are still used today in some computerized cash register systems, amongst other select applications.
Unlike colour monitors, which display text and graphics in multiple colours through the use of alternating-intensity red, green, and blue phosphors, monochrome monitors have only one colour of phosphor (mono = one, chrome = colour). All text and graphics are displayed in that colour. Some monitors have the ability to vary the brightness of individual pixels, thereby creating the illusion of depth and colour, exactly like a black-and-white television.
Monochrome monitors are available in three colours: if the P1 phosphor is used, the screen is green monochrome. If the P3 phosphor is used, the screen is amber monochrome. If the P4 phosphor is used, the screen is white monochrome (known as "page white"); this is the same phosphor as used in early television sets. An amber screen was claimed to give improved ergonomics, specifically by reducing eye strain; this claim appears to have little scientific basis.[1]
Monochrome monitors, pixel-for-pixel, produce sharper text and images than color CRT monitors. This is because on a monochrome monitor, each pixel is made up of one phosphor dot, located in the dead centre of the pixel; whereas on a colour monitor, each pixel is made up of three phosphor dots (one red, one blue, one green), none of which are in the centre of the pixel. Monochrome monitors were used in almost all dumb terminals and are still widely used in text-based applications such as computerized cash registers and Point of sale systems because of their superior sharpness and enhanced readability. Monochrome monitors are particularly susceptible to Screen burn (hence the advent, and name, of the screen saver), on account of the fact that the phosphors used are very high-intensity. Another effect of the high-intensity phosphors is an effect known as "ghosting", wherein a dim afterglow of the screen's contents is briefly visible after the screen has been blanked. This has a certain place in pop culture, as evidenced in movies such as The Matrix, amongst other places.



• Colour monitor

Colour monitor is a displays peripheral that displays more than two colour. Colour monitor have been developed trough the following paths.




• FLAT PANEL DISPLAYS

Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays that use cathode ray tubes, and are usually less than 100 mm (4 inches) thick. They can be divided into two general categories; volatile and static. In many applications, specifically modern portable devices such as laptops, cellular phones, and digital cameras, whatever disadvantages exist are overcome by the portability requirements. FEDs combine the advantages of CRTs, namely their high contrast levels and very fast response times, with the packaging advantages of LCD and other flat panel technologies. They also offer the possibility of requiring less power, about half that of an LCD system. To date, however, manufacturing problems have prevented any FED system from entering commercial production. FEDs are closely related to another developing display technology, the surface-conduction electron-emitter display, or SED.



• Electroluminescent (EL) Displays


Electroluminescence (EL) is an optical and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field. Electroluminescent Displays (ELDs) are a type of display created by sandwiching a layer of electroluminescent material such as GaAs between two layers of conductors. When current flows, the layer of material emits radiation in the form of visible light. EL works by exciting atoms by passing an electric current through them, causing them to emit photons. By varying the material being excited, the colour of the light emitted can be changed. The actual ELD is constructed using flat, opaque electrode strips running parallel to each other, covered by a layer of electroluminescent material, followed by another layer of electrodes, running perpendicular to the bottom layer. This top layer must be transparent in order to let light escape. At each intersection, the material lights, creating a pixel.



• Gas plasma displays
A plasma display panel (PDP) is a type of flat panel display common to large TV displays (80 cm or larger). Many tiny cells between just two panels of glass hold a mixture of noble gases. The gas in the cells is electrically turned into a plasma which emits ultraviolet light which then excites phosphors to emit visible light. Plasma displays should not be confused with LCDs, another lightweight flat screen display using different technology.