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The keyboard The mouse Joystick The scanner 1. Hand –held scanners 2. Flatbed scanners 3. Drum scanners Optical character reader Magnetic ink character reader The light pen Bar code readers Microphone Digital camera
The input is responsible for acceptinginput i.e., data and instructions from theuser. This work is accomplished with thehelp of input devices. Device , in general ,refers to an equipment. Over many years , many input deviceshave been built in many forms for manyspecial purposes .For instance , keyboard isused for different purpose and a mouse ora trackball is used for different purpose .
Keyboard is a typewriter like device which isused to type in the letters , digits and commands. A keyboard contains a matrix of switches (oneswitch per key).Each key , when pressed , sends adigital code to the computers that determineswhich key has been pressed e.g., if you press ‘A’when caps lock key is on , a code 01000001 issent to computer ;computer than translates thiscode to determine that you pressed ‘A’.
Advantages Reliable way of inputting text and numbers. Available in variety of formats. Disadvantages Not useful for entering some specific type of data . Very slow while accessing menu options or selectingvarious objects screen. Not much useful for enlarging or changing sizes ofwindows on screen . Very slow while moving windows or other objects.
The mouse is a pointing device with aroller on its base. Mouse controlsmovement of pointer 98also called mousepointer) on screen.When a mouse moveson a flat surface , the cursor on the screenalso moves in the direction of mouse’smovement . A mouse generally has two orthree buttons and it may or may not havea wheel.
Advantages Ideal for pointing objects/options on desktopcomputers . Most familiar and easy to use pointing device . Disadvantages Need a flat space close to computer. A mouse can’t easily be used with a laptop or anotebook or a palm top computers .
Joysticks are often used for playingcomputer games such as flightsimulators . They input directionaldata like mouse but work by switchesbeing closed as the joystick is movedleft or right and up or down .Minifinger – controlled joysticks can beused to control a laptop cursor.
Advantages Easy to learn to use. It is not costly. Disadvantages Movement is offered only in forward , backward ,left and right directions , so diagonal movementscreate problems at times .
A scanner is a device similar to a photocopier . Aphotocopier prints the given printed image/page on apaper . And a scanner creates a electronic form of theprinted image ,which can later be manipulated ,changed and modified according to the requirements .The scanners can convert any image into electronicform by shining light on to the image and sensing theintensity of reflection at every point .Scanners comein the variety of sizes from hand-held models todesktop models.
Hand – held scanners are very small whichcan be held n a hand . These are lessexpensive but less wide . Hence , in orderto scan a single page image , multiplepasses are required . But their handinessis a major advantage .
Flatbed scanners are larger and moreexpensive scanners but they definitelycreate higher quality images . Thesescanners have a flat surface an which theprinted image to be scanned , is placed .(Similar to the way a page is placed on aphotocopier). Flatbed scanners can scan apage in a single pass .
Drum scanners are medium – sizescanners with a rolling drum . Thesheet is fed through the scanners sothat the drum rolls over the entiresheet to be scanned . ( Just as thesheets are fed in a fax machines).
Advantages Flatbed scanners are very accurate and can produceimages with a far higher resolution than a digitalcamera. Any image can be convertd from paper into digitalformat and later enhanced and used in order computerdocuments . Disadvantages Images can take up a lot of memory space. The quality of the final image depends greatly uponthe quality of original documents.
An optical character reader is used to read character ofspecial type font(or fonts0 printed on conventionalpaper with conventional ink. These days , OCRs arecapable of reading/identifying handwritten text also .The printed characters are examined by passing themunder a strong light and a lens system , whichdifferentiates light(no ink) from inked areas , and alogical system which attempts to determine which ofthe possible characters is being examined .
AdvantagesOCR is faster than typing a document which is inprinted form or hand-written form.Converted text is editable in word processors.Advanced version can even recreate tables , columnsand even produce web pages.DisadvantagesYou need to buy a scanner or OCR software.It is not completely accurate and text would need proof –reading afterwards.
In this method , human readable characters areprinted on documents (such as cheques ) using aspecial magnetic ink. Special font has been set forthese characters by American Banking Association . Characters are printed using a special ink calledmagnetic ink(that contains iron oxide).MICR readsthese characters by magnetizing the ink and byexamining the shape of the character . This method ,besides saving time , also ensures the accuracy of dataentry.
Advantages Documents prepared for MICR are difficult to forge. Documents can still be read after being folded or splitetc. Disadvantages MICR readers and encoders are expensive. The system can only accept few characters.
A light pen is also a pointing device. The light penconsists of a photocell mounted in a pen-shaped tube.When the pen is brought in front of a picture elementof the screen , it senses light coming from a limitedfield of view. The light coming from the screen causesthe photocell to respond by generating a pulse . Thiselectric response is transmitted to a processor thatidentifies the pixel the light pen is pointing to.Clicking is performed by pressing the pen on thescreen . Thus , to identify a specific location, the lightpen is very useful . But the light pen provides noinformation when held over a blank part of the screenbecause it is a passive device with a sensor only.
Advantages Easy to use. Useful for programs like CAD(Computer AidedDesign) for changing shape , size , location , coloursetc, of the screen image. Can directly draw on screen. Disadvantages Not very accurate while drawing. Expensive compared to alternate pointing devices likemouse. Tiresome after long usage hours.
A bar code reader is also one of the most widely usedinput devices . As you must be aware that a bar code isa pattern of printed bars on various types of products .You may even see a bar code printed at the back coverof this book . A bar code reader emits a beam of light (generally a laser beam) which reflects off the bar codeimage . A light sensitive detector in the bar code readerthen identifies the bar code image by recognisingspecial bars at the both ends of the image .Once thebar code is identified , the bar pattern is converted intoa numeric code that can be processed later in anymanner.
Advantages Fast and reliable method of inputting data. Can even read from curved or upside downsurfaces. Disadvantages Input is limited to a number code.
We can send sound input to computer through aspecial input device called microphone or mic inshort. A mic converts the sound received intocomputer’s format , which is called digitalized soundor digital audio. A mic can work if your computer has a specialhardware known as sound card. Sound is used most often in multimedia , where thepresentation can benefit from recorded narration ,music or sound effects.
Advantages Useful for inputting audio / sounds whichcan’t be input through other available inputdevices. Disadvantages Needs specific and additional hardwarecalled soundcard which must be inserted inmotherboard.
A camera that stores images digitally rather than recordingthem on film is called digital camera. The light passing through the lens of digital camera isdigitalized by special servers that are sensitive to light . Theimage formed is stored is camera’s storage memory. Once a picture has been taken , it can be downloaded to acomputer system , and than manipulated with the graphicsprogram and printed. The big advantage of digital cameras is that making photosis both inexpensive and fast because there is no filmprocessing.
The output unit is responsible for producing theoutput in user readable form . Various output deviceslike monitor , printer , plotter etc. make the outputunit of a computer. The function of an output device is to presentprocessed data to the user . The computer sendsoutput to the monitor if the user needs to see theoutput . The output is send to the printer whenever theoutput is needed in the hard copy form. The soundoutput is processed with the help of speakers .Graphics output is processed with the help of plotters.
Monitor or screen is the most common form of outputfrom a computer . It displays information in a similarway to that shown on a television screen . The pictureon a monitor is made up of thousands of tiny coloureddots called pixels. The two most common types of monitor are a Cathode- Ray Tube (CRT) and a Liquid Crystal Display(LCD)monitor.
The CRT works in the same way asatelevision – it contains an electrongun at the back of the glass tube . Thisfires electron on the group of phosphordots , which coat the inside of thescreen . When the electrons strike thephosphor dots they glow to give thecolours .
Liquid crystal is the material used to create each pixelon the screen . The material has a special property – itcan ‘ polarise ’ light depending on the electrical chargeupon it . This feature allows the pixels to be created .Each tiny cell of liquid crystal is a pixel . TFT(Thin Film Transistor) is the device within eachpixel that sets the charge . And so sometimes they arecalled ‘Liquid Crystal Display’ referring to the materialthey use or they are called ‘TFT Displays’ referring tothe tiny transistors that make them work . LCDs usemuch less power than a normal monitor .
Advantages Relatively cheap and reliable . Can display text and graphics in a wide range of colours . As each task is processed , the results can be displayedimmediately on the screen . Quiet . Disadvantages No permanent copy to keep – the results will disappearwhen the computer is switched off . Unsuitable for hours with visual problems . Only a limited amount of information can be displayed atany one time . CRT screens are made of glass and can be very fragile .
Printer is an output device used for creatingpaper copies of output from the computer .Printers can produce text and image onpaper . There are two types of printers used . Theyare – Impact printers Non- impact printers
In these printers , there is mechanicalcontact between the print head and paper .These come in a lot of varieties such as lineprinters , drum printers , daisy wheelprinters , and dot matrix printers . Mostcommon impact printer in use today is Dotmatrix printer , which is being covered inthe coming lines .
The dot matrix printer is a most popular serialprinter i.e., it prints one character at a time . InDMPs , the printing head contains a vertical arrayof pins . As the head moves across the paper ,selected pins fire against an inked ribbon to form apattern of dots on the paper .These days 24 pinDMPs are also available in the market offeringmore quality and more features . There are 80column DMPs and 132 column DMPs available inthe market .
Advantages Low operating costs . Can print on continuous stationary . They are robust and can be used in dirty or harshconditions –you often see them in garages or factories . Using carbonated paper , DMPs can create carbon copies . Disadvantages Low resolution – print quality is too poor . Very slow –can be less than 100 characters per minute . Very noisy – can’t be used near a phone . Cnnot produce colour copies .
In these printers , there is nomechanical contact between the printhead and paper . The naturallimitations of speed inelectromechanical devices and costconsiderations have led to thedevelopment of printers called non –impact printers .
An inkjet printer is any printer that firesextrememly small droplets of the ink ontopaper to create impression of text or image .The printhead of inkjet printers containstiny nozzles through which differentcoloured inks can be sprayed onto paper toform the characters or graphic images . Theink of inkjet printer is stored in catridges .
Good resolution – usually 300-600 dots per inch . Thismeans they can print good quality results . Cheap to buy . Small – ideal for home or offic . Lighter in weight than other printers . Fast compared to a dot matrix printer . Very quiet . Can print black and white and colour on the samepage .
Slow compared to a laser printer . Colour printing can take 25-30 seconds each page . Overall , the catridges cost more per page than laserprinter catridges . Catridges need to be replaced more frequently thanthose of a laser printer . Output is ink based and will smudge if the printoutgets wet . If left unused for long periods of time , the catridgescan easily dry out .
These printers print in the same way asphotocopies do .The powered ink istransferred to paper to form a text/imagepattern . It is then fixed by heat andpressure .The laser printers are quiet and arecapable of producing very high point quality.The speed of laser printers can be upto 10-20 pages per minute . When used to printbulk of papers , the laser printer producesthe cheapest cost per page printouts .
Very high resolution – 600 to 1200 dots perinch . High quality printouts . Very fast : 10 –20 pages per minute formultiple copies . Almost silent . Running costs are low , although tonercatridges are expensive to replace , they lasta long time .
Most expensive printer type to buy especially colourlasers . Expensive to repair – lots of complex equipmentinside . Can’t use continuous or multi – part stationary tocreate carbon copies . Only A4 or A5 paper can be used in most laser printersalthough A3 is available .
Many applications require a graphicaloutput apart from printed output .Forexample , pie charts , bar charts and graphswith annotations are useful representationof information .Plotters are the outputdevices that produce good quality drawingsand graphs . There are two types of plotters :drum plotter and flat bed potter .
Advantages Drawings are of the same quality as if an expert drew them . Larger sizes of paper can be used than would be found onmost printers . Disadvantages Plotters are slower than printers , drawing each lineseparately . They are often more expensive to buy than printers . Although drawings are completed to the highest qualitythey are not suitable for text although text can be produced. There is a limit to the amount of detail these plotters canproduce . In recent years , cheaper printers that can handle A3 andA2 sized paper have resulted in a decline in the need forsmaller plotters .
Speakers receive the sound in form ofelectric current from the sound card andthen convert it to sound format . Thespeakers that are attached to the computerare similar to the ones that are connected toa stereo . The only difference is that thecomputer system’s speakers are usuallysmaller and they contain their own smallamplifier .