Presentation on theme: " A printer is an output device that produces text and graphics on a physical medium such as paper.  Printed information is often called hard copy because."— Presentation transcript:




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2  A printer is an output device that produces text and graphics on a physical medium such as paper.  Printed information is often called hard copy because the information exists physically and is a more permanent form of output than that presented on a VDU (Monitor).  Printers can be grouped into impact and non- impact printers.

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3  An impact printer forms characters and graphics on a piece of paper by striking a mechanism against an ink ribbon that physically contacts the paper. Examples are Dot-matrix and Character printers.

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4 Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to etch the symbols on paper. Examples are Inkjet, Laser, Thermal.

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5  The printing speed of a printer is usually expressed in pages per minute. Printer resolution is often expressed in dpi (dots per inch). The larger the number, the higher the resolution.  Advantages: Information produced is permanent.  Disadvantages: The time to get the printout is slow, when compared with display devices. Paper is wasted for obtaining the output. Printers are generally noisier than display devices.

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7  A dot-matrix printer is an impact printer that produces printed images with a print head striking mechanism.  Most dot-matrix printers use continuous-form paper.  These use rows (a matrix) of needles which are made to impact with an ink-ribbon to make the pattern of the required character on the paper.  Each character as a group of small dots.

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8  Tiny metal rod, also called a "wire" or "pin“.  One or two columns of dot hammers  Speeds range from 200 to 400 cps.  They are relatively cheap to buy.  The speed of a dot-matrix printer is normally measured by the number of characters per second (cps) it can print.

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9  Advantages of dot-matrix printers:  Dot-matrix printers can print both text and graphics.  Dot-matrix printers can withstand dusty environment, vibrations, and extreme temperature.  Disadvantages of dot-matrix printers:  Dot-matrix printers are generally noisy because of the striking mechanism.  Print quality of dot-matrix printers is not as good as those from ink-jet printers and laser printers

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11  An ink-jet printer in a non-impact printer that forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper.  Ink-jet printers can produce letter-quality text and graphics in both black-and-white and colours.  Printer resolution is measured in dots per inch (dpi). The speed of an ink-jet printer is measured in lines per minute (lpm).

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12  Advantages:  Medium to low purchase cost.  Almost silent printing.  Excellent quality text and colour images.  Can print overhead transparencies  Disadvantages:  High running costs.  Faster than a dot-matrix printer.  Special paper needed for best results.  Cannot produce duplicate copies while printing top copy.

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14  These work in a similar way to photocopiers.  A laser beam is used to create an electric charge which attracts special black dust to it.  The dust is then transferred to the paper to produce the printed output.  Laser printers are faster and quieter than ink-jet printers and produce a very high quality print.  They are also relatively expensive.

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15  A scanner can be used to input pictures and text into a computer. There are two main types of scanner; Hand-held and Flat-bed.

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16  A scanner is used to input pictures or text. If a picture is being input, the scanner will convert it to an image made up of a large number of dots – typically 300 dots per inch.  The number of dots per inch is a measure of the scanner’s resolution. More dots per inch means a higher resolution or better quality images. However, it also means that the size of the picture file will be larger.

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17  Hand-held scanners are small devices that are moved by hand across the document being scanned.  They are small and cheap but there are problems when scanning larger images since several scans will be needed to cover the whole page. The individual scans then have to be ‘stitched together’ by software.

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18  Advantages:  Good for inputting pictures and line art.  Good for inputting large amounts of text using OCR.  Disadvantages:  Files can be large, particularly if high resolution colour is used.  Text can be incorrect. Some characters like zero and the letter O can be confused.  Flatbed scanner has a large footprint.

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19  Flat-bed scanners look similar to photocopier machine.  It consists of a box containing a glass plate on its top and a lid that covers the glass plate.This glass plate primarily used for placing the document to be scanned.  For scanning,an A4 size document takes about 20 seconds.

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20  These scanners are capable of scanning black and white as well as colour images.  The flat bed scanners are larger in size and more expensive than the hand held scanner.

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 They usually produce better quality images.

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