Hardware

Hardware

1. Storage

2. Input

   • Scanners
   • Readers

3. Output

   • Printers
     • Non-impact
     • Impact
   • Visual display units
     • Cathode-ray tube
       • A vacuum tube with a narrow neck and a flat rectangular base. The screen is coated with a phosphor that emits light when struck by an electron beam. The neck is surrounded by electromagnets and contains an electron gun.
       • Mono-colour
         • The electron gun is dragged across the screen a line at a time so it covers every horizontal line of screen, starting at the top of the screen and finishing at the bottom. The retinal image from each phosphor dot persists in the human brain for about 0.05 seconds. If the electron gun moves faster then 0.05 seconds there will be no flickering
       • Colour
         • The screen of is made up of lines of phosphor dots arranged in triplets and each triplet consists of one red phosphor, one green phosphor, one yellow phosphor. Therefore there is an electron gun for each dot and thus the intensity of each gun determines the added colour of the phosphors.
     • Flat screen
       • LCD
         • A liquid crystal display flat screen is a matrix of liquid crystals cells and each cell constitutes one pixel when the screen is used at full resolution. For colour displays, each pixel is divided into three or four subpixels covered with colour filters for additive mixing of red, green and blue. Four-subpixel arrangements have a neutral greyscale pixel to improve brightness control
         • TFTs
           • Made using tiny thin film transistors. Each pixel of a TFT, a capacitor and the liquid crystal. The transistor acts as a switch and the capacitor as a reservoir for the electrical charge needed to create the electric field that changes the polarisation of the light passing through the liquid crystal. The capacitor can hold the charge until the the next fresh cycle.
         • Unlike CRTs monitors, LCDs display information only there native
     • Plasma screen
       • 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 ultraviolet light, which strikes phosphors on the front of the screen to emit visible light. They suffer from low contrast caused by the need to apply a constant low voltage to each pixels. Without this priming, plasma cells would suffer from poor response times similar to fluorescent light bulbs. One consequence is that pixels in the off state still emit some light, which reduces contrast. The greatest limitation of plasma screens is pixel size, typically 0.81mm. This is unsuitable for smaller monitors viewed at close range because the pixels are too blocky. Plasma screens generate a lot of heat, enough to injure people that touch them