DEFINATION:-  A display devices is a device for visual or tactile presentation of images (including text)acquired, Stored or transmitted in various forms. EX : Computer Monitor, TV Screen.  Also know as an information display

 CATHODE RAY TUBE (CRT)  LIQUID CRYSTAL DISPLAY (LCD)  PLASMA DISPLAY PANEL (PDP)  ORGANIC LIGHT EMITTING DIODE (OLED)

 Pixel  Resolution  Display Size  Viewing Angle  Response time  Brightness

 Picture Element  It is the smallest element forming an image

 No. of pixels per unit video display  Video Graphics Array (VGA) a) 720x400 pixels down in text mode b) 640x480 pixels down in graphics mode

 Measured as distance from one corner to the diagonally opposite corner  Usually measured in INCHES.

 It is angle from which the screen can be seen from side  It is larger for CRT as compared to LCD

 The minimum time necessary to change a pixel’s color or brightness

 The amount of light emitted from the display ( more specifically known as luminance)

 CRT display works on :  Electron emission  Electrons are emitted from the Cathode tube  Phosphorescence  It is the emission of visible light, when electron beam strikes phosphor material.

 Cathode  Grid  Focusing anode  Accelerating anode  Aquatic coating 1.Electron guns 2.Electron beams 3.Focusing coils 4.Deflection coils 5.Anode connection 6.Mask for separating beams for red, green, and blue part of displayed image 7.Phosphor layer with red, green, and blue zones 8.Close-up of the phosphor-coated inner side of the screen

 Offers greater resolution  Widest viewing angle  It is cheap as compared to LCD,PLASMA display

 Thickness is much larger.  Cannot be used for smaller display, like watches.  View area is less than the offered monitor size.  It is more heavier.

 A Liquid Crystal Display is a thin, flat display device made up of any number of pixels arrayed in front of a light source or reflector. It uses very small amounts of electric power, and is suitable for use in battery-powered electronic devices

 When electric current was passed through the LCD panel the liquid crystals are aligned with the first polarized glass encountered and will make 90 degree twist when approaching the other polarized glass at the end

 When this happens the light from the fluorescent backlight is able to pass through and thus giving us a lighted pixel on the monitor.  When there is no electric current the liquid crystals will not twist and thus the light will not pass through and a black pixel will be shown.  The reason we see the colored images are due to the color filter light passes through the filtered cells creates the colors.

 Brightness  Produces very bright images due to high peak intensity. Very suitable for environments that are brightly lit.  Power Consumption  Energy efficient. Consume less than 1/3 the power of a comparable CRT. Consume less electricity than a CRT and produce little heat.  Physical Aspects  Take up about 40% less desk space. LCDs are thin and compact.  Screen Shape  Completely flat screen.  Sharpness  At the native resolution, the image is perfectly sharp. Adjustments are required at all other resolutions which can result in measurable degradation to the image.

 Aspect Ratio  The aspect ratio and resolution are fixed.  Contrast  Lower contrast than CRTs due to a poor black-level.  Color and Gray-Scale Accuracy  Color saturation is reduced at low intensity levels due to a poor black- level. Images are satisfactory, but not accurate due to problems with black- level, gray-scale and Gamma.  Cost  Considerably more expensive purchase price than comparable CRTs.  Resolution  Works best at the native resolution. The native resolution can not be changed. All other resolutions require adjusting procedures which can cause considerable deterioration of the image.  Viewing Angle  Restricted viewing angles. Viewing angles affect the brightness, contrast and colors shown. Wide angles can lead to contrast and color reversal.

 A plasma display panel (PDP) is essentially a collection of very small fluorescent-type lamps, each a few tenths of a millimeter in size  The plasma display itself is a simple device consisting of two parallel glass plates separated by a precise spacing of some tenths of a millimeter and sealed around edges

 Slim profile  Can be wall mounted  Less bulky than rear-projection televisions  Produces deep blacks allowing for superior contrast ratio  Wider viewing angles than those of LCD; images do not suffer from degradation at high angles unlike LCDs

 Heavier screen-door effect when compared to LCD or OLED based TVs  Susceptible to screen burn-in and image retention, although most recent models have pixel orbiter  Phosphors lose luminosity over time, resulting in gradual decline of absolute image brightness newer models are less susceptible to this, having lifespan exceeding 100,000 hours, far longer than older CRT technology  Generally do not come in smaller sizes than 37 inches  For those who wish to listen to AM radio, or are Amateur Radio operators Hams or Shortwave Listeners SWL, the Radio Frequency Interference RFI from these devices can be irritating or disabling.

 OLEDs are special because they are made-up of organic polymer molecules (otherwise known as plastic) allowing light to emit when a voltage is applied

 Voltage is applied across the OLED device allowing electron to travel from the cathode through the emissive layer to make positively charged electron holes in the conductive layer where the anode draws those electrons.  Quite simple, the anode is drawing electrons through the emissive layer to provide positive electron holes in the conductive layer  Then the positive holes and the electrons collide and recombine which leads to a drop in the electron energy level as visible light radiations is emitted

 They have the potential to be able to be produced much more cheaply than conventional LED’s, LCD’s and plasma televisions using processes derived from ink-jet printing  Improved range of colors and brightness's compared to LCD and plasma displays  Potentially very energy efficient  They can be deposited on large substrates enabling large areas to be illuminated  Lighter than LED’s  Flexible  Can produce a true black and infinite contrast ratios

 In computing, a printer is a peripheral which produces a hard copy (permanent readable text and /or graphics) of documents stored in electronic form, usually an physical print media such as paper or transparencies

 Dot matrix printer  Inkjet printer  Laser printer

 The printer head is made up of a row of pins – usually 9 or 25 pins forming a vertical bar. To form a letter, the pins are “fired "in quick succession to press the ribbon against the paper.

 low purchase cost.  can handle multipart forms.  cheap to operate, just new ribbons.  rugged and low repair cost.

 noisy.  low resolution. You can see the dots making up each character.  Not all can do colour.  Colour looks faded and streaky.

 The Inkjet Printer is a common type of printer which works by spraying a tiny drop of ink at paper. The technology is probably best explained by this animated picture.  The printing works the same way as the dot-matrix print head above. the only difference is that we are now using droplets of ink instated of hammers.  Inkjet works by having a print catridge with a series of tiny electrically-heated chambers constructed by photolithography  When the bubble, surplus ink is sucked back up from the printing surface. the ink’s surface tension pumps another charge of ink into the chamber through a narrow channel attached to an ink reservoir

 Images are produced on a drum  A laser beam sets electrical charge on dots on the drum  Magnetically charged power called toner flies to the electrified dots on the drum  The drum rolls the toner on the paper  A second drum burns the toner on the paper

 The final stage is for the paper to pass through very hot “rollers "which “melt "the ink on the paper  The heat “seals” the ink on to the paper instantly making sure that you do not get smudging or crinkling as you can with other printer types