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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Character printers are of two types:1.Dot matrix printer2.Daisy Wheel printer

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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 Printer

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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 printer

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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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