OUTPUT DEVICES An output device is an electro mechanical device which converts machine readable information into human readable form. The output devices display the processed information which is in the form of digital signals by converting them into graphical, alphanumeric or audio-visual form.Types of output device:- Output produced by the output devices can be of the following forms.1) Text :- Textual form of output consists of characters(letters, numbers, punctuation marks.)2) Graphics:- Graphics are digital representation of non-tetxual information such as drawings, charts, photographs and animation.3) Audio:- Audio includes music, speech or any sound.4) Video:- Video consists of images that are played back at a speed that provide the illusion of full motion. Generally there are two basic categories of output. The output which can be understood and used by the individuals, and which is stored on secondary storage devices so that the data can be used as input for further processing. The output which can be easily understood and used by the individuals are of the following forms. 1) Hard copy: The physical form of output is known as hard copy. It refers to the recorded information copied from a computer onto the paper or some other durable surfaces. Hard copy output is permanent and relatively stable form of output.2) Soft copy: The electronic version of an output which resides in the computer memory and/or on the disk, is known as soft copy. It is not a permanent form of output. It is transient and is usually displayed on the screen. It is not tangible.

CLASSIFICATION OF OUTPUT DEVICES: Printers, plotters and microfilms are the commonly used hard copy output devices while monitor, voice systems, projectors are soft copy output devices.1) Printer:- A printer prints information and data from the computer onto a paper. The printer prints 80 to 132 columns of characters in each line and prints either on single sheet or a continuous roll of paper. The quality of a printer is determined by the clarity of a print it can produce, that is its resolution.Resolution is used to describe the sharpness and clarity of an image. The higher the resolution, the better the image. Printers are divided into 2 categories:a) Impact Printer: It uses pins or hammers that press on inked ribbon against the paper to make a mark on the paper.Charteristics of Impact Printers: There is physical contact with the paper to produce an image. They are cheap and useful for bulk printing. They can withstand dusty environment, vibrations. Ideal for printing multiple copies. They are slow and noisy.i. Dot matrix printer(Wire matrix printer): It prints one character at a time as patterns of dots. The speed is measured in characters per second(cpi), which can vary from 200 to more than 500 cpi. Print quality is determined by number of pins. They are bi-directional but can print only in black and white. In dot- matrix printer, the paper is pressed against a rubber coated cylinder and is pulled forward as printing progresses characters are formed by moving the electro- magnetically driven print head across the paper, which strikes the printer ribbon which produces characters made up of dots which are small.ii. Diasy wheel printer: It is named so because the print head of this printer resembles a daisy flower with the printing arms that appear like the petals of the flower. They produce high resolution output but cannot print graphics. These are slower and expensive that dot matrix printers. These printers have print heads composed of metallic or plastic wheels. A raised character is placed on the tip of each of the daisy wheels petals. The print wheel is rotated around until the desired character is under the print hammer. The petal is struck from behind by print hammer which strikes the character, pushing it against ink ribbon and onto the paper.iii. Drum printer: It is a line printer. It uses special tractor-fed paper with pre punched holes along each side. This allows a continous high speed printing. In this printer, multiple hammers strikes multiple type elements against the paper almost simultaneously and thus prints one line operation. Drum printer involves a large rotating drum mounted horizontally positioned in front of inked ribbon which is positioned in front of the paper. Drum contains characters moulded onto its surface in columns, which will be printed by rotating the drum. b)Non impact printer: It forms characters and images without making direct physical contact between the printing mechanism and the paper. Characteriscts are: They are faster and quicker than impact printer. The produce high quality graphics. They cannot print carbon copies.

i. Inkject printers: It places small droplets of ink onto paper to create an image. It has a print catridge with a electrically heated chambers which are attached to the print head with a series of small nozzles that spray ink onto the surface of the paper. As print head moves back and forth across the page, softwage gives instructions regarding type and quality of colours and also the position where the dots of ink should be sprayed.ii. Laser printer: A laser printer provides the highest quality text and images for personal computers. They are known as page printers. Resolution of most printer is 600dpi. They are quiet and fast able to print 4 32 text only pages per minutes. They can print more than 2000 lines/min. they are faster than ink- jet printer but are more expensive than other printers. In laser printer a rotating mirror inside the printer causes the beam of a laser to sweep across the photoconductive drum. At the point where the laser strikes the surface of the drum, it creates a dot of positive change. These points are represented by a black dot, which will be printed on the paper. Then the black powder called toner contained in a container is negatively charged and it clings to the positive areas of the drum surface when the powder pattern gets fixed, drum is rotated and the paper is fed into the drum surface via a pressure roller. This pressure roller transfers the black toner onto the paper.Hydra printer: Hybrid document reproduction apparatus(HYDRA) printer popularly known as all-in-one printer, is a device that consolidates the capabilities of multiple devices in one machine. It may include some or all of the devices like printer, scanner, photocopier and fax machine. Print speed, maximum resolution, memory card compatibility, scanner resolution, fax speed are the features to be considered while evaluating these printers.

2)Plotters: a plotter is a pen based output device that is attached to a computer for making vector graphics. It is used to draw high resolution charts, graphs, maps and other line based diagrams. It draws lines using a pen. Multi colour plotter uses different coloured pens to draw different colours. A plotter draws much crisper lines and graphics. Plotters are expensive as compared to printers.Types of plotters: There are 2 typesi. Drum plotter: Here, the paper on which the design is to be printed is placed over a drum. These plotters consists of one or more pen that are mounted on a carriage, which is either clockwise or anti-clockwise direction under the control of plotting instructions sent by the computer.ii. Flat- bed plotter: It consists of a stationary horizontal plotting surface on which the paper is fixed. The pen is mounted on a carriage which can move in all directions to draw lines. These plotters are instructed by the computer about the movement of pens in the X-Y co-ordinates on the page. The heart of the plotter is printer head assembly which consists of a horizontal bar and pen in use attached to the head assembly holding. Plotters create plots by moving a pen under computer control over a drafting paper. The computer instructions received by a plotter consists of a colour and beginning and end co-ordinates for a line.3. Computer Output Microfilm(COM): It is an extremely high speed, low cost process, which records computer generated information directly from the computer tape or catridge to a miniaturized microfilm media. The microfilm product is in roll format which can be duplicated rapidly and inexpensively. The image area of the copy is reduced upto 1/40 of its original size, retaining its original clarity. COM results in material, space and equipment savings along with mailing costs and information retrieval savings. It facilitates indexing to access information. The disadvantage is that it is expensive to install COM and microfilms cannot be read without the assistance of a special reader device. A microfilm output is used for distribution of airline schedules, medical X-ray.

Creating microfilms: Microfilms can be created in following ways.1. Photographic process: It uses a microfilm camera for producing microfilms. When the original documents are fed through a camera, it captures document into a reduced size photo. Then rolls of films are removed from the camera for further processing and development. The processed images can be rolled on film rolls or cut into sections and loaded to flat microfiche holders.2. Non photographic process: here computer output is read onto the magnetic tape, after which data printed on microfilm by using microfilm recorder.4.MONITOR:A computer monitor is a TV like display attached to the computer on which the output can be displayed and viewed. The computer monitor can be a monochrome display(uses one colour) or a colour display. Monitor are available in various sizes like 14,15,17,19 and 21 inches. The size of the display is described based on two parameters.i. Aspect ratio It is the ratio of the width of the display screen to the height i.e ratio of the vertical points to the horizontal points.ii. Screen size which is measured diagonally (in inches), the distance from one corner to the opposite corner.In monitor image is created and displayed using configuration of dots known as Picture element or pixels or pels.

The screen quality depends on 3basic qualities1) Resolution:- It refers to the number of pixels in the horizontal and vertical directions on the screen. Move the number of dots, sharper will be the image.2) Dot pitch:- It is the measurement of the diagonal distances between two like coloured pixels on the display screen. Smaller the dot pitch sharper will be on the image. It is measured in millimeter.3) Refresh rate:- It is the number of times per second the pixels made from phosphor are recharged so that their glow remains bright. Refresh rate is measured in hertz.

Colour Depth:- It also refered to as bit depth, refers to the number of bits assigned to each pixel in the image and the number of colours that can be created from those bits. An 8 bit colour is known as pseudocolour, 16 bit mode as high colour and 24 bit mode is called true colour. In 1981, IBM introduced colour graphics adapter(CGAS) which had 4 colour. In 1984, IBM introduced enhanced graphics adapter(EGA) display which enabled monitors to display 16 different colours. In 1987, video graphics array(VGA) was introduced. In 1990, extended graphics array(XGA) was introduced. Nowadays i.e. uses super video graphics array(SVGA).Cathode Ray Tube Monitors:- Most computer monitors uses CRT technology. A beam of electrons emitted by an electron gun passes through focusing and deflection systems that direct the beam towards specified positions on the phosphor coated screen. The phosphor then emits a small spot of light at each position contacted by the beam. When the electron beam strikes the phosphor, light is emitted for short period of time which is known as persistence.

Displaying graphics on a CRT:- Two classes of computer graphics displays are used:-1. Raster Scan Display:- In this, electron beam is swept across the screen, one row at a time from top to bottom. Picture definition is stored in a refresh buffer or frame buffer which is displayed on the screen one row at a time.2. Random Scan Display:- Here CRT has electron beam directed only to the parts of screen where picture is to be drawn. It draws a picture one line at a time and they are referred to as vector, stroke- writing or calligraphic display. Picture definition is stored in refresh display file. Colour Display On a CRT:- CRT monitor displays colour pictures by using a combination of phosphors that emit coloured lights.Two basic techniques for processing colour display are as follows:1) Beam penetration:- It is used with random scan display. In this system, two layers of phosphor are coated on inner side of CRT screen. Displayed colour depends on how far the electron beam penetrates into the phosphor layers.2) Shadow masking:- It is used in raster scan system. A shadow mask CRT has 3 phosphor colour dots and 3 electron gun and a shadow mask grid behind phosphor coated screen. When three beams pass through a hole in the shadow mask they activate a dot triangle which appears as a small colour spot on the screen.Liquid Crystal Display Monitors:- LCD monitor uses liquid crystals to display images. An LCD screen is a collection of multiple layers. The polarized light passes through a layer that contains thousands of liquid crystal blobs aligned in tiny containers called cells. These cells are aligned in rows across screen making up pixels.Differences between CRT and LCD:-i. SIZE:- LCD is lightweight compared to CRT.ii. RESOLUTION:- LCD works in single resolution while CRT for many resolutions.iii. Pixel Density:- Pixel density of LCD is not as tight as dot pitch in CRT.iv. Brightness:- Phosphor of a CRT is not as bright as LCD florescent light.v. Power consumption:- LCD consumes less power than CRT.vi. Flicker:- LCD runs at much slower refresh rate than CRTvii. Pixel response time:- the time taken by a pixel to change its state is called pixel response time. CRT has fast pixel response time than LCD.viii. Viewing angle:- a CRT can be viewed at almost any angle but LCD is best viewed head on.ix. Viewing area:- viewing area of CRT is less than its advertised area. But LCD is measured exactly.x. Cost:- cost of LCD are high than CRT.

Other Types of Monitors1) Plasma display- also known as thin panel,is constructed by filling a gas between the two glass plates2) Thin film Electroluminescent display- it is similar to plasma display but space between the glass plate is filled with phosphorescent substance 5.Voice Response System:- It has an audio response device which produces audio output. These sounds are prerecorded in a computer system. Each sound has a unique code. When an enquiry is sought, computer responds in digital form which is sent to voice devices that unscramble the digital information and produces sound messages to requesting computer. There are 2 approaches for the system:1. Synthesis by analysis where the system analyses the input of actual human voice speaking words, stores and process the spoken sounds and reproduces them as needed.2. Synthesis by rule which applies complex set of linguistic rules to create artificial speech. Computer system provides audio output with the addition of two components - a speech synthesis that does the speaking and a screen reading software.6.Projectors:- Screen image projector is an output device which is used to project information from a computer onto a large screen. It is used for classroom training or conference room.Types of projector:-1. LCD projector; It refers to liquid crystal display. It contains three separate LCD glass panels.2. DLP projector: DLP stands for Digital Light Processing. It uses a single digital mirror device(DMD) chip that has thousands of tiny mirrors each representing a single pixel.

LCD versus DLP:1. An LCD controls red, green and blue independently. User can adjust brightness and contrast of each colour channel. But in DLP colour is fixed.2. LCD delivers sharper image than a DLP.3. LCD is more light efficient and produces higher lumen output than DLP.4. DLP light engine consists of single chip rather than three LCD panels.5. LCDs are known for their visible pixel structure.7.Electronic Whiteboard:- It is an interactive presentation device that works electronically to display digital images, drawings and text in different colours. White board is mounted on the wall and is connected to a computer and a projector. Projector projects the computer desktop on the wall and is connected to a computer and a projector . Projector projects the computer desktop on the whiteboard and user can interact with it using electromagnetic pens, fingers or pointing device.Categories of whiteboard:-1. Touch based:- It allows the user to use finger to interact with it.2. Pen based:- It uses an electromagnetic pen that alters electrical signals produced by the board.3. Wii remote, IR pen based:- A wii Remote, infrared(IR) pen based whiteboard works on sound electronic and optical principals.

8.Headphones and Headsets:- Headphone is an audio device equipped with a pair of speakers which are attached to a headstrap worn by the users. It allows the users only to listen. A headset is a combination of one or two speakers and the microphone attached to a headstrap. Speaker allows the person to hear and the microphone allows to communicate.

9.Terminals:- Computer terminals is a special unit that can perform as both input and output. A terminal is an I/O device that uses a keyboard for input and a monitor for output. A terminal is also known as Video Display terminal. A terminal can be categorized as:1) Dumb terminals:- It refers to a terminal that has no processing or programming capabilities. It is used for simple data entry or retrieval task.2) Smart terminal:- It has built in processing capability and memory but does not have its own storage capacity. They are found in LAN in offices.3) Intelligent terminals:- It has memory and in built microprocessor, hence also called user programmable terminal.

INPUT DEVICES keyboard layout