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Printers
Produce Hardcopy of computer output such as data, text, graphics (drawings or charts).
Most computers are designed to receive data in parallel from the computer i.e. 8 bits at a time.
Printers have to be connected to the parallel port on the computer, also called LPT1 (Line Pinter 1)
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Computer Printer Differ in the following aspects:Character Printer:
Print one character at a timeLine Printer:
Print one line at a timePage Printer:
Print one page at a time
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Variety of printing technologies are possible:Dot matrixDaisy WheelInk jetLaser
Some printers can only handle textsWhereas some printers can handle texts and
graphicsVariety of standard exists for control codes,
which are commands sent from computer to printer to turn on effects such as underlining and emboldening
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Main Differences between the printers depends on :The quality of outputThe ability to print graphicsThe printing speed
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Character PrinterPrint one character at a timeThey are slow printerCapable of printing at the rate of 30 to 300
characters per second (cps)Advantages:Low costDisadvantages:Slow speedMakes a lot of noise while printing
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Character PrinterCharacter printers were very popular in the
past but these days they are being replaced with inkjet printers.
Inkjet printers have the following advatages over character printer.
good printing quality,makes less noisefast printing speedproduce multicolour printouts.
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Dot Matrix Printer (Impact matrix printer)Dot Matrix Printers have 9 or 24 pins
arranged in the form of matrixTo print a character on the paper, the built in
microprocessor activates the appropriate pins in the print head to move forward and hit the printer ribbon, which is placed against a paper.
As a result the shape of the character appears on the paper.
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Dot Matrix PrinterDot Matrix printer form the shape of the
character by a number of dots and not with the character shape itself.
Therefore the print quality is low
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Daisy wheel PrinterThe print head of a daisy wheel printer is a
circular wheel about 3 inches in diameter with arms/spokes.
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Daisy wheel PrinterThe character shapes are embossed at the
outer end of the arms. The shape of the printer wheel resembles the
petals of a daisy flower, hence it is named daisy wheel printer.
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Daisy wheel PrinterTo print a character, the daisy wheel rotates
so that the required character is positioned just in front of the printer ribbon.
Now the spoke/arm containing the desired character is hit by a hammer and strikes the ribbon leaving an impression on the paper placed behind the ribbon.
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Movement of all these parts is controlled by microprocessor in the printer.
AdvantagesPrint quality is high because exact shape of the
character hits the ribbon to leave an impression on paper.
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Line printerPrint one line at a timeFaster than character PrinterHeavy duty printers and they can print at the
rate of 2000 lines per minute.Two types of line printers are:1.Chain Printer2.Drum Printer
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Chain PrinterPrint characters are contained in a chain
which is moved continuously at a rapid rate by two geared pulleys
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Chain PrinterCircuitry within the printer senses when the
correct character appears at the desired print position on the page
At that point the hammer strikes the page.This action presses the paper against the
ribbon and leaves the impression of that character on the paper.
When the requirement of the printed line are fulfilled, the printer carriage control moves the page to the next line position.
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Drum printerThe principal of the drum printer is similar to
that of the chain printer.All the characters are engraved along the
circumference of the drum, and 132 print positions are available.
NOTE: Character printer and line printer are called impact printer because they use electro-mechanical mechanism which causes the character shape to strike against the paper and leave an image of the character on the paper.
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NON-IMPACT PRINTERLaser Printer:Laser printers are page printer, as they print
entire page at a timeResembles photocopier in size and
appearance.They are very fast, speed being around 8
pages per minute.Silent in operation
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NON-IMPACT PRINTERPrint quality is good to that of daisy printerResolution of current models is 600 dots per
inch (dpi).Some of the latest versions offer 1400 dpi.Laser printers can handle graphics as well as
textPrint quality is higher than that of inkjet
printersExpensive
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Laser printerMechanism:Consists of Laser light, roller and toner (ink)A sheet of paper is fed from a tray into the
machine and receives an electrostatic charge across its surface.
The laser beam traces the computer output (text, graphics) as a pattern of tiny dots on the paper.
During this process, it removes the electrostatic charge from the points where the beam strikes the paper.
The paper then receives the fine toner across its surface which sticks to the points with no charge.
After passing between rollers, the paper come out, heated and dried at the front of the machine.
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LASER PRINTERPROS:Due to the printing process, laser printers can print
documents at a much faster rate than inkjet printers.Price by price comparisons tends to favour laser
printers over inkjet papers for documents that are not graphically complex.
CONS:Warm-up times delay the initial printing start-up
time.Toner costs are higher than inkjet ink cartridges.Because the toner has an electrostatic charge, toner
will stick to most anything, making toner leaks
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INKJET PRINTERThe inkjet printer works by spraying variable size ink dropPROS: Ideal for printing photographs and other image intensive
documents. Inkjets can print onto many types of paper, from cheap
office paper to high-end glossy photograph paper.Most inkjet cartridges can be refilled and reused, Which
saves money.
CONS:Brand new inkjet cartridges tend to be a bit pricey. Inkjet ink is typically water-based, thus making prints
highly at risk to water-damage and fading. Ink cartridges need frequent cleaning, which most printers
perform automatically.
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