The input and output device

BY-SRISHTI SAXENACLASS-IX

THE INPUT AND OUTPUT UNIT

The keyboardThe mouseJoystickThe scanner1. Hand –held scanners2. Flatbed scanners3. Drum scannersOptical character readerMagnetic ink character readerThe light penBar code readersMicrophoneDigital camera

CONTENTS OF INPUT UNIT…

Monitors1. Cathode ray tube2. Liquid crystal displayPrinters Impact printers Non-impact printers1. Inkjet printers2. Laser printersPlotters Speakers

CONTENTS OF OUTPUT UNIT…

The input is responsible for accepting input i.e., data and instructions from the user. This work is accomplished with the help of input devices. Device , in general , refers to an equipment.

Over many years , many input devices have been built in many forms for many special purposes .For instance , keyboard is used for different purpose and a mouse or a trackball is used for different purpose .

The Input Unit…

Keyboard is a typewriter like device which is used to type in the letters , digits and commands . A keyboard contains a matrix of switches (one switch per key).Each key , when pressed , sends a digital code to the computers that determines which key has been pressed e.g., if you press ‘A’ when caps lock key is on , a code 01000001 is sent to computer ;computer than translates this code to determine that you pressed ‘A’.

The Keyboard…

AdvantagesReliable way of inputting text and numbers.Available in variety of formats.DisadvantagesNot useful for entering some specific type of

data .Very slow while accessing menu options or

selecting various objects screen.Not much useful for enlarging or changing sizes

of windows on screen .Very slow while moving windows or other objects.

Advantages and Disadvantages…

The mouse is a pointing device with a roller on its base. Mouse controls movement of pointer 98also called mouse pointer) on screen.When a mouse moves on a flat surface , the cursor on the screen also moves in the direction of mouse’s movement . A mouse generally has two or three buttons and it may or may not have a wheel.

The Mouse…

AdvantagesIdeal for pointing objects/options on

desktop computers .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 a notebook or a palm top computers .


Joysticks are often used for playing computer games such as flight simulators . They input directional data like mouse but work by switches being closed as the joystick is moved left or right and up or down .Mini finger – controlled joysticks can be used to control a laptop cursor.

Joystick…

AdvantagesEasy to learn to use.It is not costly.DisadvantagesMovement is offered only in forward ,

backward , left and right directions , so diagonal movements create problems at times .


A scanner is a device similar to a photocopier . A photocopier prints the given printed image/page on a paper . And a scanner creates a electronic form of the printed image ,which can later be manipulated , changed and modified according to the requirements . The scanners can convert any image into electronic form by shining light on to the image and sensing the intensity of reflection at every point .Scanners come in the variety of sizes from hand-held models to desktop models.

The Scanners…

Hand – held scanners are very small which can be held n a hand . These are less expensive but less wide . Hence , in order to scan a single page image , multiple passes are required . But their handiness is a major advantage .

Hand – Held Scanners …

Flatbed scanners are larger and more expensive scanners but they definitely create higher quality images . These scanners have a flat surface an which the printed image to be scanned , is placed . (Similar to the way a page is placed on a photocopier). Flatbed scanners can scan a page in a single pass .

Flatbed Scanners…

Drum scanners are medium – size scanners with a rolling drum . The sheet is fed through the scanners so that the drum rolls over the entire sheet to be scanned . ( Just as the sheets are fed in a fax machines).

Drum Scanners…

AdvantagesFlatbed scanners are very accurate and can

produce images with a far higher resolution than a digital camera.

Any image can be convertd from paper into digital format and later enhanced and used in order computer documents .

DisadvantagesImages can take up a lot of memory space.The quality of the final image depends greatly

upon the quality of original documents.


An optical character reader is used to read character of special type font(or fonts0 printed on conventional paper with conventional ink. These days , OCRs are capable of reading/identifying handwritten text also . The printed characters are examined by passing them under a strong light and a lens system , which differentiates light(no ink) from inked areas , and a logical system which attempts to determine which of the possible characters is being examined .

Optical Character Reader…

Advantages OCR is faster than typing a document which is

in printed form or hand-written form. Converted text is editable in word

processors. Advanced version can even recreate tables ,

columns and 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 are printed on documents (such as cheques ) using a special magnetic ink. Special font has been set for these characters by American Banking Association .

Characters are printed using a special ink called magnetic ink(that contains iron oxide).MICR reads these characters by magnetizing the ink and by examining the shape of the character . This method , besides saving time , also ensures the accuracy of data entry.

Magnetic Ink Character Reader…

AdvantagesDocuments prepared for MICR are difficult to

forge.Documents can still be read after being

folded or split etc.DisadvantagesMICR readers and encoders are expensive.The system can only accept few characters.

Advantages and Diadvantages…

A light pen is also a pointing device. The light pen consists of a photocell mounted in a pen-shaped tube .When the pen is brought in front of a picture element of the screen , it senses light coming from a limited field of view. The light coming from the screen causes the photocell to respond by generating a pulse . This electric response is transmitted to a processor that identifies the pixel the light pen is pointing to. Clicking is performed by pressing the pen on the screen . Thus , to identify a specific location, the light pen is very useful . But the light pen provides no information when held over a blank part of the screen because it is a passive device with a sensor only.

The Light Pen…

AdvantagesEasy to use.Useful for programs like CAD(Computer Aided

Design) for changing shape , size , location , colours etc, of the screen image.

Can directly draw on screen.DisadvantagesNot very accurate while drawing.Expensive compared to alternate pointing

devices like mouse.Tiresome after long usage hours.


A bar code reader is also one of the most widely used input devices . As you must be aware that a bar code is a pattern of printed bars on various types of products . You may even see a bar code printed at the back cover of this book . A bar code reader emits a beam of light ( generally a laser beam) which reflects off the bar code image . A light sensitive detector in the bar code reader then identifies the bar code image by recognising special bars at the both ends of the image .Once the bar code is identified , the bar pattern is converted into a numeric code that can be processed later in any manner.

Bar Code Readers…

AdvantagesFast and reliable method of inputting

data.Can even read from curved or upside

down surfaces.DisadvantagesInput is limited to a number code.


We can send sound input to computer through a special input device called microphone or mic in short. A mic converts the sound received into computer’s format , which is called digitalized sound or digital audio.

A mic can work if your computer has a special hardware known as sound card.

Sound is used most often in multimedia , where the presentation can benefit from recorded narration , music or sound effects.

Microphone…

AdvantagesUseful for inputting audio / sounds

which can’t be input through other available input devices.

DisadvantagesNeeds specific and additional

hardware called soundcard which must be inserted in motherboard.


A camera that stores images digitally rather than recording them on film is called digital camera.

The light passing through the lens of digital camera is digitalized by special servers that are sensitive to light . The image formed is stored is camera’s storage memory.

Once a picture has been taken , it can be downloaded to a computer system , and than manipulated with the graphics program and printed.

The big advantage of digital cameras is that making photos is both inexpensive and fast because there is no film processing.

Digital Camera…

The output unit is responsible for producing the output in user readable form . Various output devices like monitor , printer , plotter etc. make the output unit of a computer.

The function of an output device is to present processed data to the user . The computer sends output to the monitor if the user needs to see the output . The output is send to the printer whenever the output is needed in the hard copy form. The sound output is processed with the help of speakers . Graphics output is processed with the help of plotters.

The Output Unit…

Monitor or screen is the most common form of output from a computer . It displays information in a similar way to that shown on a television screen . The picture on a monitor is made up of thousands of tiny coloured dots called pixels.

The two most common types of monitor are a Cathode - Ray Tube (CRT) and a Liquid Crystal Display(LCD) monitor.

Monitors…

The CRT works in the same way as atelevision – it contains an electron gun at the back of the glass tube . This fires electron on the group of phosphor dots , which coat the inside of the screen . When the electrons strike the phosphor dots they glow to give the colours .

Cathode- Ray Tube Monitor…

Liquid crystal is the material used to create each pixel on the screen . The material has a special property – it can ‘ polarise ’ light depending on the electrical charge upon 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 each pixel that sets the charge . And so sometimes they are called ‘Liquid Crystal Display’ referring to the material they use or they are called ‘TFT Displays’ referring to the tiny transistors that make them work . LCDs use much less power than a normal monitor .

Liquid Crystal Display Monitor…

AdvantagesRelatively cheap and reliable .Can display text and graphics in a wide range of

colours .As each task is processed , the results can be

displayed immediately on the screen .Quiet .DisadvantagesNo permanent copy to keep – the results will

disappear when the computer is switched off .Unsuitable for hours with visual problems .Only a limited amount of information can be

displayed at any one time .CRT screens are made of glass and can be very

fragile .


Printer is an output device used for creating paper copies of output from the computer . Printers can produce text and image on paper .

There are two types of printers used . They are –

Impact printersNon- impact printers

Printers…

In these printers , there is mechanical contact between the print head and paper . These come in a lot of varieties such as line printers , drum printers , daisy wheel printers , and dot matrix printers . Most common impact printer in use today is Dot matrix printer , which is being covered in the coming lines .

Impact Printers…

The dot matrix printer is a most popular serial printer i.e., it prints one character at a time . In DMPs , the printing head contains a vertical array of pins . As the head moves across the paper , selected pins fire against an inked ribbon to form a pattern of dots on the paper .These days 24 pin DMPs are also available in the market offering more quality and more features . There are 80 column DMPs and 132 column DMPs available in the market .

Dot Matrix Printers…

AdvantagesLow operating costs .Can print on continuous stationary .They are robust and can be used in dirty or harsh

conditions –you often see them in garages or factories .Using carbonated paper , DMPs can create carbon

copies .DisadvantagesLow 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 no mechanical contact between the print head and paper . The natural limitations of speed in electromechanical devices and cost considerations have led to the development of printers called non – impact printers .

Non – Impact Printers…

An inkjet printer is any printer that fires extrememly small droplets of the ink onto paper to create impression of text or image . The printhead of inkjet printers contains tiny nozzles through which different coloured inks can be sprayed onto paper to form the characters or graphic images . The ink of inkjet printer is stored in catridges .

Inkjet Printers…

Good resolution – usually 300-600 dots per inch . This means 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

same page .

Advantages…

Slow compared to a laser printer .Colour printing can take 25-30 seconds each

page .Overall , the catridges cost more per page

than laser printer catridges .Catridges need to be replaced more

frequently than those of a laser printer .Output is ink based and will smudge if the

printout gets wet .If left unused for long periods of time , the

catridges can easily dry out .

Disadvantages…

These printers print in the same way as photocopies do .The powered ink is transferred to paper to form a text/image pattern . It is then fixed by heat and pressure .The laser printers are quiet and are capable of producing very high point quality .The speed of laser printers can be upto 10-20 pages per minute . When used to print bulk of papers , the laser printer produces the cheapest cost per page printouts .

Laser Printers…

Very high resolution – 600 to 1200 dots per inch .

High quality printouts .Very fast : 10 –20 pages per minute

for multiple copies .Almost silent .Running costs are low , although

toner catridges are expensive to replace , they last a long time .

Advantages…

Most expensive printer type to buy especially colour lasers .

Expensive to repair – lots of complex equipment inside .

Can’t use continuous or multi – part stationary to create carbon copies .

Only A4 or A5 paper can be used in most laser printers although A3 is available .

Disadvantages…

Many applications require a graphical output apart from printed output .For example , pie charts , bar charts and graphs with annotations are useful representation of information .Plotters are the output devices that produce good quality drawings and graphs . There are two types of plotters : drum plotter and flat bed potter .

Plotters…

AdvantagesDrawings are of the same quality as if an expert drew

them .Larger sizes of paper can be used than would be found on

most printers .DisadvantagesPlotters are slower than printers , drawing each line

separately .They are often more expensive to buy than printers .Although drawings are completed to the highest quality

they are not suitable for text although text can be produced .

There is a limit to the amount of detail these plotters can produce .

In recent years , cheaper printers that can handle A3 and A2 sized paper have resulted in a decline in the need for smaller plotters .


Speakers receive the sound in form of electric current from the sound card and then convert it to sound format . The speakers that are attached to the computer are similar to the ones that are connected to a stereo . The only difference is that the computer system’s speakers are usually smaller and they contain their own small amplifier .

Speakers…

THE END…

The input and output device

Education

advantages flatbed scanners

scanners comein

moreexpensive scanners

scanners sothat

mouse joystick

mouse moveson

final image

pointing device