1cd Output


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1cd Output

  1. 1. Output Devices
  2. 2. Printers <ul><li>Factors affecting choice </li></ul><ul><ul><li>Volume of output </li></ul></ul><ul><ul><ul><li>High volume require fast, heavy-duty printer </li></ul></ul></ul><ul><ul><li>Quality of print required </li></ul></ul><ul><ul><li>Location of printer </li></ul></ul><ul><ul><li>Are multiple copies required? </li></ul></ul><ul><ul><li>Is colour required? </li></ul></ul>
  3. 3. Types of Printer <ul><li>Dot Matrix </li></ul><ul><ul><li>Impact Printer - Print head has 9 or 24 pins </li></ul></ul><ul><ul><li>Pins strike paper through a ribbon. </li></ul></ul><ul><ul><li>24 pins give better print quality – dots closer </li></ul></ul><ul><ul><li>NLQ (Near Letter Quality) obtained by printing each line twice, which second pass slightly displaced so as to fill any spaces. </li></ul></ul><ul><ul><li>Printers are often bi-directional </li></ul></ul><ul><ul><li>Very versatile </li></ul></ul><ul><ul><li>Colour possible via 4-colour ribbon – but quality not too good </li></ul></ul><ul><ul><li>Can be very noisy </li></ul></ul>
  4. 4. Types of Printer <ul><li>Inkjet Printer </li></ul><ul><ul><li>Very popular – often bundled with PC </li></ul></ul><ul><ul><li>Cheap with very good resolution, particularly on special papers </li></ul></ul><ul><ul><li>Droplets of ink are fired at the paper </li></ul></ul><ul><ul><li>Large areas of colour may get the page too wet unless special paper is used </li></ul></ul><ul><ul><li>Colour printing can be quite expensive </li></ul></ul>
  5. 5. Types of Printer <ul><li>Laser Printer </li></ul><ul><ul><li>More accessible now as prices come down </li></ul></ul><ul><ul><li>Similar process to photocopier with toner images being fused onto the paper by heat and pressure </li></ul></ul><ul><ul><li>Very high quality </li></ul></ul><ul><ul><li>Virtually silent </li></ul></ul><ul><ul><li>Colour option can be very expensive </li></ul></ul>
  6. 6. Plotters <ul><li>Used for high quality line drawings </li></ul><ul><ul><li>Building plans </li></ul></ul><ul><ul><li>Circuit diagrams </li></ul></ul><ul><li>Pen (Vector plotters) </li></ul><ul><ul><li>Draw images using point-to-point data, moving pen over the paper. </li></ul></ul><ul><ul><li>Low in price </li></ul></ul><ul><li>Penless (Raster plotters) </li></ul><ul><ul><li>Electrostatic, thermal or laser plotters </li></ul></ul><ul><ul><ul><li>Required for high-density images </li></ul></ul></ul><ul><ul><ul><li>Maps </li></ul></ul></ul><ul><ul><ul><li>Assemble drawings for machines </li></ul></ul></ul>
  7. 7. VDU <ul><li>Three attributes: size, colour and resolution. </li></ul><ul><li>It has its own RAM to store the image on screen </li></ul><ul><li>Amount of RAM will determine resolution and number of colours that can be displayed. </li></ul><ul><li>Resolution </li></ul><ul><ul><li>Number of pixels used to represent a full screen </li></ul></ul><ul><li>Colours </li></ul><ul><ul><li>Dependent on number of bits available for each pixel </li></ul></ul><ul><ul><ul><li>If only 1 bit, only 2 colours can by displayed </li></ul></ul></ul><ul><ul><ul><li>8 bits will allow 256 colours </li></ul></ul></ul><ul><ul><ul><li>16 bits (2 bytes) will allow 65,536 colours per pixel </li></ul></ul></ul><ul><ul><ul><li>800x600 with 65,536 colours requires approx 1Mb of video RAM </li></ul></ul></ul>
  8. 8. Communicating with the CPU <ul><li>Buses </li></ul><ul><ul><li>Used to transfer data, addresses and control signals to various components of the computer </li></ul></ul><ul><li>Internal Bus </li></ul><ul><ul><li>Connect the various registers and internal components of the CPU </li></ul></ul><ul><li>External Bus </li></ul><ul><ul><li>Connect the CPU to main memory and the I/O units </li></ul></ul><ul><li>Interface Units </li></ul><ul><ul><li>Because I/O units vary in terms of their speed, mode of operation and so on, they are not connected directly to the CPU. Each device will have its own interface unit </li></ul></ul>
  9. 9. Data Transmission – Parallel & Serial <ul><ul><li>A parallel bus with 8 lines can transfer 1 byte at a time </li></ul></ul><ul><ul><li>A serial bus only transfers 1 bit at a time. </li></ul></ul><ul><ul><li>Common serial interface is the 25-pin RS232C cable used to connect an external modem to a PC </li></ul></ul><ul><ul><li>Most mouse interfaces used to be a 9-pin serial interface, although now they are usually a PS2 connection and increasingly USB (Universal Serial Bus connection) </li></ul></ul><ul><ul><ul><li>USB offers speeds of up to 12 megabit per second </li></ul></ul></ul><ul><ul><li>In serial mode only 1 line is used for data, the other lines are used for control signals, grounding etc </li></ul></ul><ul><ul><li>Parallel is faster because 8 bits are transferred simultaneously. </li></ul></ul><ul><ul><li>Parallel only available over short distances (2 – 3 metres) </li></ul></ul>
  10. 10. Buffering & Spooling <ul><li>Buffers </li></ul><ul><ul><li>Memory used to hold data during I/O transfers to and from I/O devices </li></ul></ul><ul><ul><li>CPU operates much faster than printer so input and output have to controlled independently </li></ul></ul><ul><ul><ul><li>Once I/O is initiated by CPU, a special I-O channel takes control . </li></ul></ul></ul><ul><ul><li>Many printers will have their own memory buffer </li></ul></ul><ul><li>Spoolers </li></ul><ul><ul><li>These speed up communication between devices which operate at different speeds </li></ul></ul><ul><ul><li>Output for the printer, for example, may be spooled (written) to disk. </li></ul></ul><ul><ul><li>When the printer becomes free, output will be printed </li></ul></ul><ul><ul><li>This is the method employed on a network . </li></ul></ul>
  11. 11. Installing Hardware Devices <ul><li>Scanners, printers, mouse, soundcard etc </li></ul><ul><ul><li>When these devices are installed on to a computer system they usually require a device driver to be installed. </li></ul></ul><ul><ul><li>You may also need to assign a port for a printer </li></ul></ul><ul><ul><li>Most devices can now be installed via Plug and Play on Windows systems. </li></ul></ul><ul><ul><li>A printer driver carries information specific to the printer model – fonts and control sequences, etc. </li></ul></ul><ul><ul><li>The driver will translate the font and formatting information in your document into a form that the printer can understand. </li></ul></ul>