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AS Computing - Output Devices
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Case of 3 pages for the course AS Computing at HSDC
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Output DevicesVisual display units
Cathode ray tube (CRT) - A cathode ray tube, is a vacuum tube, which is used to create
images in computers or televisions etc. It does this by accelerating and then deflecting
electron beams onto the screen which results in the image. There are 3 electron guns that
shoot the electron beams through the CRT. The beams are deflected by a varying magnetic
field. There are 3 electron guns because there are 3 primary colours (red, yellow and blue)
that are needed to create every other colour. Cathode ray tubes have been superseded by
LCD or plasma screens. However, they are still used in some older screens, specialist
machines, or just because they are much cheaper than LCD screens etc.
http://en.wikipedia.org/wiki/Cathode_ray_tube
Flat screen (TFT) – TFT is a thin-film-transistor liquid-crystal display, which is used in LCD
screens to improve the qualities like contrast and legibleness. Flat screen displays are thin
screens that use CRT’s, they are far lighter and thinner than the original ‘box’ screen (CRT).
This type of screen is used in many products – mobile phones, laptops, tablets, digital
cameras etc.
http://en.wikipedia.org/wiki/Flat_panel_display and http://en.wikipedia.org/wiki/TFT_LCD
Plasma screen- Plasma display panels (PDP) is a type of flat panel display usually used in
30inch or larger screens. They are called this because of the use of electrically charged
ionized gases in small cells. This is the same technology that is used in fluorescent lamps.
Plasma displays go up to 1000 lux or higher, with very good picture quality. However, the
power consumption isn’t constant, as the screen takes more power if the picture is brighter
or more active.
http://en. wikipedia.org/wiki/Plasma display
Speech Output – The most common use of speech outputs, are in speech generating (SGD’s)
devices. Used by people with severe speech impairments or on computers to read out the
text on the screen for visually impaired people. SGD’s work by the user typing what they
want to say into a keypad then the device converts it into an automated voice.
http://en.wikipedia.org/wiki/Speech-generating_device
Impact Printer- Impact printers work by physically hitting, and forcing the ink onto the page
that it’s printing. It either hits a ribbon that in turn hits the paper, or it directly hits the
paper. This type of printer is obsolete now with all the new laser, or more efficient printers,
but during it’s time it was widely used.
, http://en.wikipedia.org/wiki/Impact_printer#Impact_printers
Non-Impact Printers
Inkjet printing (Line by line) – Inkjet printing works by creating a digital image by propelling
droplets of ink onto the printing surface (paper, plastic etc.). Inkjet printing is the most
widespread and popular type of printing at the moment, they can range from home printers
to big industrial size printing.
http://en.wikipedia.org/wiki/Inkjet_printing
Laser Printers – Laser printing works by passing a laser over a (rotating)
charged drum, which then collect the toner and transfers the image to paper.
This is then heated to permanently fix the image onto the paper. Laser
printing produces a very high quality of text and graphics.
[ Drum rotates, and the laser charges it at where it needs to be printed, then
the drum rotates and the toner is attracted the charged parts of the drum, the drum rotates
and prints the toner (ink) onto the paper. Then the paper is heated which fixes the ink into
the page properly. ]
http://en.wikipedia.org/wiki/Laser_printer
Bitmap and TrueType fonts – TrueType fonts is the original format for fonts (and outline
font standard) developed my Apple and Microsoft in the late 1980’s. It became the common
format for fonts on both Mac OS and Microsoft Windows. A bitmap is a form of image file
format used to store digital images. It is also a way of storing a binary image, that is when
each pixel in the image is coded as either 1 or 0, to represent black or white, or any other 2
colours.
http://en.wikipedia.org/wiki/Bitmap and http://en.wikipedia.org/wiki/TrueType
Multifunction Printers – A multifunction printer is a device that incorporates the uses of
multiple different devices. So the device could act as a scanner, fax machine,
photocopier and printer etc. There are three main types of multifunction printers, AIO
(small and designed for home/home office use), SOHO MFP (a small independent machine,
usually with print, copy and scan functions, used in small office or home offices), or an
Office MFP (a mid-sized freestanding unit to be used in the office, with many functions, as
well as networked document storage with security etc.).
http://en.wikipedia.org/wiki/Multifunction_printer
Photo Printers – Photographic printing is the process of producing an image to be viewed
on chemically sensitized paper. These types of printers work by using enlarger and a digital
exposure unit, such as a lightjet printer.
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