Output Devices

Output Devices - A peripherals used to present or get the results of a computers work to the outside.

 Displays
Cathode Ray Tube (CRT) - Is a vacuum tube with a narrow neck and a flat rectangular base. The screen is coated on the inside with a phosphor that emits light when struck by an electron beam. The electron beam is produced by an electron gun which dragged across the screen a line at a time so it covers every horizontal line of the screen. CRT's use three different types of electron gun, red, green and blue. the screen is made up of phosphor dots which are arranged in triplets and each triplet consists of a red, green and blue phosphor.

Liquid Crystal Display (LCD) - Electric crystals can change the polarisation of light when an electric field is applied to them. A LCD display is a matrix of liquid crystal cells and each cell constitutes a pixel when the screen is used at full resolution.For colour displays each pixel is divided into three or four sub pixels covered with coloured filters for additive mixing of red, blue and green.

Plasma Screen - Plasma screens are ideal for large displays. Each pixel is controlled by a miniature fluorescent light. When the control voltage is applied the gas becomes plasma and releases UV light, which strikes phosphors on the front of the screen to emit visible light. Plasma screens generate a lot of heat, enough to burn if you touch them.

Printers
Ink jet Printer - An ink jet printer produces coloured output by printing a line at a time. Coloured ink jet printers use three colours; Cyan, Magenta and Yellow. Ink jet printers can be slow when printing in the highest resolution  and the ink can smudge. For the very best quality, special paper is required. Also you have to buy cartridges every couple of months, which are expensive.

Laser Printer - A laser printer prints a whole page at a time. It prints high quality text and graphics on plain paper. A negative charge is applied to the photosensitive drum at the heart of the printer. One or more laser beams are directed onto the rotating drum's surface. The lasers are turned on and off at positions determined by the bitmap data stored in the raster memory. This causes the negative to be neutralised or reversed at positions corresponding to the black parts of the page to be printed. The charged surface of the drum is exposed to toner, fine particles of dry plastic powder which is mixed with carbon black. The toner particles are given a negative charge so they attach to the positive charged parts of the drum. Which is then transferred to paper.

Impact Printer (Dot Matrix) - A Printer that only prints in black & white and can only print text, it uses a similar structure of a type writer to print the text, as it stamps the letters onto the page. They use a ink ribbon to mark the paper  with an impression of a character. In a Dot Matrix printer the ribbon is struck by up to 24 metal pins that form the outline of a character.

Plotter - A plotter moves a pen across paper in a continuous movement so that the two-dimensional drawing can be made. The pen is lifted when it is not drawing on the paper and is lowered to draw and mark the paper. In a drum plotter, a roll of paper at least one meter wide is fed over a drum. The pen is located above the paper and is constrained to move the length of the drum in a straight line. A drum plotter is used to produce engineering drawings (blueprints) to a very large scale, it is also used for producing posters for billboards for example.

Other
Sound - Usually given out via speakers