4

Input Output Media

1.  What are input and output devices?

Ans.: An input device is an electromechanical device that allows the user to feed information into the computer for analysis, storage, and to give commands to the computer. Data and instructions are entered into the computer's memory through an input device. It captures information and translates it into a form that can be processed and used by the other parts of the computer. Some examples of input devices are keyboard, mouse, trackball, joystick, scanner, etc.

After processing the input data, the computer provides the results with the help of output devices. An output device converts machine-readable information into human-readable form. The basic functioning of the output device is just the opposite of the input device, that is, the data are fed into the computer system through the input device while the output is taken out from the computer through the output device. However, the output, which comes out from the CPU, is in the form of digital signals. The output device displays the processed information by converting them into graphical, alphanumeric, or audio-visual form. Some examples of output devices are printers, plotters, monitor, projectors, etc.

2.  Explain the roles of various input and output devices in the computer system.

Ans.: The processing of the data by the computer system can be viewed as a three-phase process as follows:

1. Data input via an input device.
2. Processing of data.
3. Data output via an output device.

Input devices play a major role in the processing of any data via the computer system because the output of the computer is always based on the given input. Generally, data that are given to the input devices is raw. Therefore, it is the function of the input devices to manipulate the raw data and then send it for further processing. The preparation of the computerized input is the initial step in the creation of useful output. This output must be supplied to the outside world, which is done through output devices.

3.  Explain the working of the keyboard.

Ans.: A keyboard is the most common data entry device. Using a keyboard, the user can type text and commands. It is designed to resemble a regular typewriter with a few additional keys. Data are entered into computer by simply pressing keys. The layout of the keyboard has changed very little ever since it was introduced. In fact, the most common change in its technology has simply been the natural evolution of adding more keys that provide additional functionality. The number of keys on a typical keyboard varies from 84 to 104 keys. It is the easiest input device, as it does not require any special skill. Usually, it is supplied with a computer so no additional cost is incurred. The maintenance and operational cost of the keyboard is also less. However, using the keyboard for data entry may be a slow process because the user has to manually type all the text. In addition, it can be difficult for people suffering from muscular disorder.

Working of Keyboard

A keyboard is a series of switches connected to a small keyboard microprocessor that monitors the state of each switch and initiates a specific response to a change in state. When the user presses a key, it causes a change in the amount of current flowing through the circuit associated specifically with that key. The keyboard microprocessor detects this change in current flow. By doing this, the processor can tell when a key has been pressed and when it is being released. Depending upon which key's circuit carries a signal to the microprocessor, the processor generates the associative code, known as scan code, of the key and sends it to the operating system. A copy of this code is also stored in the keyboard's memory. When the operating system reads the scan code, it informs the same to the keyboard and the scan code stored in the keyboard's memory is then erased.

Initially, the processor filters all the tiny current fluctuations out of the signal and treats it as a single key press. If the user continues to hold down a key, the processor determines that the user wishes to send that character repeatedly to the computer. In this process, the delay between each instance of character can normally be set in the operating system, typically ranging from 2 to 30 characters/s (cps).

4.  What do you understand by the term ‘pointing device’? Give some examples of commonly used pointing devices.

Ans.: A pointing device is a device that does not require keying of characters, instead the user can move a cursor on the screen and perform move, click, or drag operations. It is used to communicate with the computer by pointing to locations on the monitor screen. Some of the commonly used pointing devices are mouse, trackball, joystick, light pen, touch screen, and trackpad.

5.  Explain the mouse, its working, and discuss its different operations.

Ans.: A mouse is a small handheld pointing device with a rubber ball embedded at its lower side and buttons on the top. Usually, it contains two or three buttons, which can be used to input commands or information. It may be classified as a mechanical mouse and an optical mouse, based on the technology it uses. A mechanical mouse uses a rubber ball at the bottom surface, which rotates as the mouse is moved along a flat surface, to move the cursor. It is the most common and least expensive pointing device. An optical mouse uses a light beam instead of a rotating ball to detect movement across a specially patterned mouse pad. As the user rolls the mouse on a flat surface, the cursor on the screen also moves in the direction of the mouse's movement. It is pricier than their mechanical counterparts but is accurate and often do not need a mouse pad.

Working of Mouse

A mechanical mouse has a rubber ball at the bottom. When the user moves the mouse along the flat surface, the ball rolls. The distance, direction, and speed of the ball's motion is tracked. These data are used by the computer to position the mouse pointer on the screen. Inside the mouse are three rollers. One of them, which is mounted at a 45° angle to the other two, is spring loaded. This roller is usually the smallest of the three. It is there simply to hold the ball against the other two rollers. The other two rollers are usually larger, and of different colour. These rollers are mounted at a 90° angle to one another. One roller measures how fast the ball is turning horizontally, and the other measures how fast it is turning vertically. When the ball rolls, it turns these two rollers. The rollers are connected to axles, and the axles are connected to a small sensor that measures how fast the axle is turning. Both sets of information are passed to the electronics inside the mouse. This little processor, usually consisting of little more than a single chip, uses the information to determine how fast the mouse itself is moving, and in what direction. This information is passed to the computer via mouse cord, where the operating system then moves the pointer accordingly.

Some of the common mouse actions are listed as follows:

	Pointing: It means moving the mouse pointer to position it on an object like icon or a menu item on the screen.
	Click: The action of pressing down a mouse button (usually the left one) and releasing it is known as a click. The term comes from the fact that pressing and releasing most mouse buttons makes a clicking sound.
	Right-click: Clicking of the right mouse button is known as right-click. In Microsoft Windows, right-clicking often produces a ‘pop-up’ menu depending on the object selected, offers options that can lead the user to open a program, cut or copy, create a shortcut, or display the properties of the selected object.
	Double-click: It refers to the action of clicking the mouse button twice in rapid succession without moving the mouse between clicks. Double-clicking is used to perform an action such as starting an application or to open a folder.
	Drag and drop: It refers to the action of clicking and holding down the mouse button while moving the mouse (drag), and then releasing the mouse button (drop). It is used to move the object (e.g., a file) or selected text to the new position. If the mouse has several buttons, use the leftmost button unless instructed otherwise.

6.  What is the purpose of a trackball?

Ans.: Trackball is a pointing device that resembles a ball nestled in a square cradle and serves as an alternative to a mouse. In general, it is as if a mouse is turned upside down. It has a ball that can be rotated by fingers in any direction, the cursor moves accordingly. The size of the ball in the trackball varies from as large as a cue ball to as small as a marble. Since it is a static device, instead of rolling the mouse on the top of the table the ball on the top is moved by using fingers, thumbs, and palms. This pointing device comes in various shapes and forms but with the same functions. The three shapes, which are commonly used, are a ball, button, and square. Like the mouse, a trackball is also used to control cursor movements and the actions on a computer screen. However, it remains stationary on the surface, only the ball is moved with the fingers or palm of the hand. By moving just the fingers and not the entire arm, the user can get more precision and accuracy, which is why many graphic designers and gamers choose to use trackball instead of the mouse.

7.  Write in brief on the following:

(a) Joystick

(b) Light pen

(c) Trackpad

Ans.: (a) Joystick: It is a pointing device that moves in all directions and controls the movement of the cursor. The basic design of a joystick consists of a stick that is attached to a plastic base with a flexible rubber sheath. This plastic base houses a circuit board that sits beneath the stick. The electronic circuitry measures the movement of the stick from its central position and sends the information for processing. It also consists of buttons that can be programmed to indicate certain actions once a position on the screen has been selected using the stick. It offers three types of control: digital, glide, and direct. Digital control allows movement in a limited number of directions such as up, down, left, and right. Glide and direct controls allow movements in all directions (360°). Direct control joysticks have the added ability to respond to the distance and speed with which the user moves the stick. The various applications in which joystick is used are flight simulators, playing computer games, training simulators, CAD/CAM (computer-aided design/computer-aided manufacturing) systems, and for controlling industrial robots.

(b) Light pen: It is sometimes called a mouse pen. It is a handheld electro-optical pointing device which when touched to or aimed closely at a connected computer monitor, will allow the computer to determine where on that screen the pen is aimed. It facilitates drawing images and selects objects on the display screen by directly pointing to the objects. It is a pen-like device, which is connected to the machine by a cable. Although named light pen, it actually does not emit light but its light-sensitive diode would sense the light coming from the screen. The light coming from the screen causes the photocell to respond by generating a pulse. This electric response is transmitted to the processor that identifies the position to which the light pen is pointing. With the movement of the light pen over the screen, the lines or images are drawn.

Using light pen, users can interact more easily with applications, in modes such as drag and drop, or highlighting. It is used directly on the monitor screen and it does not require any special hand/eye coordinating skills. It is perfect for applications where desk space is limited, in harsh workplace environments, and any situation where fast accurate input is desired. It is very useful to identify a specific location on the screen. However, it does not provide any information when held over a blank part of the screen. It is economically priced and requires little or no maintenance.

(c) Trackpad: It is also referred as touchpad. It is a stationary pointing device that works by sensing the movement of fingers across a small sensitive surface (1.5 or 2 inches) and translating them into the pointer movement on the screen. It is generally used in laptops but can also be connected to the PC through a cord. It is also equipped in personal digital assistants (PDAs) and media players such as iPod. Typically, it also consists of two or three buttons that work as mouse buttons. Many trackpads are also strike sensitive, that is, user can tap on trackpad to perform operations like selecting an object, maximizing/minimizing the window, etc.

8.  Explain in detail how does a touch screen work.

Ans.: A touch screen is a special kind of input device that allows the direct selection of a menu item or the desired icon with the touch of finger. Essentially, it registers the input when a finger or other object is touched to the screen. It is normally used when information has to be accessed with minimum effort. However, it is not suitable for input of large amounts of data. Typically, it is used in information-providing systems like the hospitals, airlines and railway reservation counters, amusement parks, etc.

Working of Touch Screen

A basic touch screen has three main components: a touch sensor, a controller, and a software driver (Figure 4.1). The touch sensor or panel is a clear glass panel with a touch-responsive surface. It is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen. There are several different touch sensor technologies in the market today, each using a different method to detect touch input. These methods are optical, acoustical, and electrical methods. In optical method, the infrared (IR) beams interlace the surface of the screen and when a light beam is broken, that particular location is recorded. In acoustical method, the ultrasonic acoustic waves pass over the surface of the screen and when the wave signals are interrupted by some contact with the screen, the location is recorded. In electrical method, the panel has an electrical current going through it and touching the screen causes a voltage change, which is used to determine the location of the touch to the screen.

The controller connects the touch sensor and the computer. It takes information from the touch sensor and translates it into information that a computer can understand. The driver is a software update for the computer system that allows the touch screen and the computer to work together. It tells the operating system how to interpret the touch event information that is sent from the controller.

Figure 4.1 Components of a Touch Screen

9.  Explain the following input devices in detail with their advantages and disadvantages:

(a) Speech recognition system

(b) Webcam

(c) Optical character recognition (OCR)

(d) Optical mark recognition (OMR)

(e) Magnetic ink character recognition (MICR)

(f) Bar code reader

Ans.: (a) Speech recognition system: It is one of the most interactive systems to communicate with the computer. The user can simply instruct the computer with the help of a microphone (along with speech recognition software) to perform a task. It is the technology by which sounds, words, or phrases spoken by humans are converted into digital signals, and these signals are transformed into computer-generated text or commands. Most speech recognition systems are speaker-dependent, so they must be separately trained for each individual user. It learns the voice of the user, who speaks isolated words repeatedly. Then, these voiced words are recognizable in the future.

Speech recognition is gaining popularity in the corporate world among non-typists, people with disabilities, and business travellers who tape-record information for later transcription. The computer-based speech-recognition systems can be used to create text documents such as letters or e-mail, to browse the Internet, and to navigate among applications by voice commands. It has relatively high accuracy rates. It allows the user to communicate with the computer directly without using a keyboard or a mouse. However, as compared to other input devices, the reliability of speech recognizer is less. Sometimes, it is unable to differentiate between two similar sounding words such as see and sea. It is also not suitable for noisy places.

(b) Webcam: It is the short form of web camera. It is a portable video camera, which captures live video or images that may be viewed in real time over the network or the Internet. It is just a small digital camera that is either inbuilt in computer (in most laptops) or can be connected through USB port. It is normally placed on top of the PC monitor or laptop so as to capture images of the user while he/she is working on the computer. Nowadays, a wide variety of webcams are available. According to its varied capabilities and features, it is classified into two categories: streaming and snapshot. A streaming webcam captures moving images (about 30 images/s), thus creating a streaming video—a web video that plays on the computer immediately as its data arrive via network; the recipient need not download the video. However, a high-speed Internet connection is needed to transfer the smooth video and the image quality is also comparatively poor. On the other hand, a snapshot webcam captures only still images (usually, once every 30 s) and refreshes it continuously. It produces better quality images and is easier to configure than streaming videos.

The popularity of webcams is increasing day-by-day due to its unlimited uses. The most popular use of webcam is in videoconferencing to provide real-time communication where a group of people can see and interact with each other. It can be used with various messenger programs like Yahoo and Windows Live Messenger. It is cheap, compact, and easy to use and install. It is affordable because of its low manufacturing cost. The major drawback of using webcam is that it produces only real-time images and cannot be used unless attached with the PC.

(c) Optical character recognition (OCR): It is a software that scans the text document. This means that the OCR software translates the bitmap image of text to the ASCII codes that the computer can interpret as letters, numbers, and special characters. Because of OCR, data entry becomes easier, error-free, and less time consuming. However, it is very expensive and if the document is not typed properly, it will become difficult for the OCR to recognize the characters. Furthermore, except for tab stops and paragraph marks, most documents formatting are lost during text scanning. The output from a finished text scan will be a single column editable text file. This text file will always require spell checking and proof reading as well as re-formatting to get the desired final layout.

(d) Optical mark recognition (OMR): It is the process of detecting the presence of intended marked responses. A mark registers significantly less light than the surrounding paper. Optical mark reading is done by a special device known as optical mark reader. In order to be detected by the OMR reader, a mark has to be positioned correctly on the paper and should be significantly darker than the surrounding paper. The OMR technology enables a high-speed reading of large quantities of data and transferring these data to the computer without using a keyboard. Generally, this technology is used to read answer sheets (objective type tests). In this method, special printed forms/documents are printed with boxes, which can be marked with dark pencil or ink. These forms are then passed under a light source and the presence of dark ink is transformed into electric pulses, which are transmitted to the computer.

OMR has a better recognition rate than OCR because fewer mistakes are made by machines to read marks than in reading handwritten characters. Large volumes of data can be collected quickly and easily without the need for specially trained staff. Usually, an OMR reader can maintain a throughput of 1500–10,000 forms/hour. However, the designing of documents for OMR is complicated and the OMR reader needs to be reprogrammed for each new document design. OMR readers are relatively slow because the person putting marks on the documents must follow the instructions precisely. Any folding or dirt on a form may prevent the form from being read correctly. In addition, it requires accurate alignment of printing on forms and needs a paper of good quality.

(e) Magnetic ink character recognition (MICR): It is used to recognize the magnetic ink characters. These characters are printed using special ink, which contains iron particles that can be magnetized. MICR reads the characters by examining their shapes in a matrix form and the information is then passed on to the computer. For example, these special characters can be seen on the bottom of a cheque.

The banking industry prefers MICR to OCR as MICR gives extra security against forgeries such as colour copies of payroll cheques or hand-altered characters on a cheque. If a document has been forged, say a counterfeit cheque produced using a colour photocopying machine, the magnetic-ink line will either not respond to magnetic fields, or will produce an incorrect code when scanned using a device designed to recover the information in the magnetic characters. The reading speed of the MICR is also higher. This method is very efficient and time saving for data processing.

(f) Bar code reader: Bar code is a machine-readable code in the form of a pattern of parallel vertical lines of varying widths. It is commonly used for labelling goods that are available in supermarkets and numbering books in libraries. This code is sensed and read by a bar code reader using reflective light. The information recorded in bar code reader is then fed into the computer, which recognizes the information from the thickness and spacing of bars. Bar code reader is either handheld or fixed-mount. Handheld scanners are used to read bar codes on stationary items. With fixed-mount scanners, items having a bar code are passed by the scanner—by hand as in retail scanning applications or by conveyor belt in many industrial applications.

Bar code data correction systems provide enormous benefits for just about every business with a bar code data-collection solution; capturing data is faster and more accurate. A bar code scanner can record data 5–7 times faster than a skilled typist. A bar code data entry has an error rate of about 1 in 3 million. Bar coding also reduces cost in terms of labour and revenue losses resulting from data collection errors. Bar code readers are widely used in supermarkets, department stores, libraries, and other places. Bar code can be seen on the back cover of certain books and greeting cards. Retail and grocery stores use a bar code reader to determine the item being sold and to retrieve the item price from a computer system.

10.  With the help of diagram, explain how a speech recognition system works.

Ans.: A speech recognition system consists of a number of components and together they convert the human spoken words into computer-generated text and commands (Figure 4.2). The system works like when a person speaks, the speech recognition software captures the sound through a microphone and converts it to a digital signal. The signals coming out from the microphone are analog waves. These analog waves are converted into digital signals by the computer's sound card. The speech recognition software analyses the digital pattern to find matches with known sounds contained in a database, and then passes the recognized words to an application such as Microsoft Word or WordPerfect. Part of that database consists of predefined sound patterns—a one-size-fits-all vocabulary for recognizing speech from as many different voices as possible. The rest is built when a user trains the software by repeating keywords so it can recognize the user's distinctive speech patterns.

Figure 4.2 Speech Recognition System

11.  Discuss scanners along with its types.

Ans.: A scanner is an input device that converts a document into an electronic format that can be stored on the disk. The electronic image can be edited, manipulated, combined, and printed by using the image-editing software. It is also called optical scanner as it uses a light beam to scan the input data. Most of the scanners come with a utility program that allows it to communicate with the computer and save the scanned image as a graphic file on the computer. Moreover, it can store images in both greyscale and colour mode. The two most common types of scanners are as follows:

1. Handheld scanner: This scanner performs the scanning of the document very slowly from the top to the bottom with its light on. It consists of light emitting diodes, which are placed over the document to be scanned. In this process, all the documents are converted and then stored as an image. While working, the scanner is dragged very steadily and carefully over the document at a constant speed without stopping, or jerking in order to obtain best results. It is widely used where high accuracy is not of much importance. The size of the handheld scanner is small. It comes in various resolutions, up to about 800 dpi (dots per inch) and is available in either greyscale or colour. Furthermore, it is used when the volume of the documents to be scanned is low. It reads the data on price tags, shipping labels, inventory part number, book ISBNs, and so on.
2. Flatbed scanner: This scanner looks similar to a photocopier machine. It consists of a box containing a glass plate on its top and a lid that covers the glass plate. This glass plate is used for placing the document to be scanned. The light beam is placed below the glass plate and when it is activated, it moves horizontally from left to right. After scanning one line, the light beam moves in order to scan the next line and the procedure is repeated until all the lines are scanned. For scanning, an A4 size document takes about 20 s. These scanners can scan black and white as well as colour images. The flatbed scanner is larger in size and more expensive than the handheld scanner. However, it usually produces better quality images because it employs better scanning technology.

12.  Differentiate between hard copy and soft copy outputs.

Ans.: The outputs, which can be easily understood and used by human beings, are of the following two forms:

1. Hard copy: The physical form of an output is known as hard copy. In general, it refers to the recorded information copied from a computer onto paper or some other durable surface such as microfilm. Hard copy output is permanent and a relatively stable form of output. This type of output is also highly portable. Paper is one of the most widely used hard copy output media. The principal examples are printouts, whether text or graphics from printers.
2. Soft copy: The electronic version of an output, which usually resides in the computer memory and/or on the disk, is known as soft copy. Unlike hard copy, soft copy is not a permanent form of output. It is transient and is usually displayed on the screen. This kind of output is not tangible, that is, it cannot be touched. Soft copy output includes audio and visual form of output, which is generated using a computer. In addition, textual or graphical information displayed on a computer monitor is also the soft copy form of output.

13.  What is the usage of printer? Write some characteristics of impact and non-impact printers. Give examples of each.

Ans.: A printer prints information and data from the computer onto a paper. Generally, the printer prints 80 or l32 columns of characters in each line, and prints either on single sheets or on a continuous roll of paper, depending upon the printer itself. It is divided into the following two categories:

1. Impact printer: It uses pins or hammers that press an inked ribbon against the paper to make a mark on the paper. Each hammer is embossed with a specific shape that is transferred onto the paper through the inked ribbon thereby producing a printed character. Some impact printers can print only one character at a time while others can print an entire line. The three most commonly used impact printers are dot matrix printers, daisy wheel printers, and drum printers. Some characteristics of impact printers are as follows:

   a. There is physical contact with the paper to produce an image.

   b. It is relatively cheap. The primary recurring costs for this printer is the ink ribbon and papers.

   c. Due to being robust and low cost, it is useful for bulk printing.

   d. It can withstand dusty environment, vibrations, and extreme temperature.

   e. It is ideal for printing multiple copies (i.e., carbon copies) because it can easily print through many layers of paper.

   f. Due to its striking activity, it is very noisy.

   g. Since it is mechanical in nature, it tends to be slow.

2. Non-impact printers: Unlike impact printers, a non-impact printer forms characters and images without making direct physical contact between printing mechanism and paper. In this printer, the print head does not make contact with the paper, and no inked ribbon is required. Ink can be sprayed against the paper and then heat and pressure are used to fuse a fine black powder into the shape of a character. The major technologies competing in the market of non-impact printers are ink-jet and laser. Some characteristics of non-impact printers are as follows:

   a. It is faster because it has fewer moving parts.

   b. It is quieter because there is no striking mechanism involved and only few moving parts are used.

   c. It possesses the ability to change typefaces automatically.

   d. It produces high-quality graphics.

   e. It cannot print carbon copies.

14.  What are the important considerations while classifying printers?

Ans.: Today, printers are the most commonly used output devices and therefore, there are many considerations to classify a wide variety of printers. Some of them are as follows:

	Quality of printing: This measure is determined by the clarity of a print, which a printer can produce, that is, by its resolution. Resolution is used to describe the sharpness and clarity of an image. The higher the resolution, the better the image. For printers, the resolution is measured in dots per inch (dpi). The more dots per inch, the better will be the quality of image. Suppose, if a printer has a resolution of 600 dpi, it means that the printer is capable of printing 360,000 dots per square inch. The printers having resolutions between 300 dpi and 600 dpi are used for ordinary day-to-day printing jobs, whereas printers having resolutions between 1200 and 2000 dpi are used for top-quality professional printing such as in publishing industries.
	Approach of printing: The approach being used for printing the documents whether there is physical contact with the paper (such as impact printers) or there is no direct physical contact between printing mechanism and paper (such as non-impact printers). Printers that are having physical contact with paper are noisier as compared with printers that do not have direct physical contact.
	Speed of printing: This is among one of the most important consideration of classifying the printers. The speed of printers can vary from 40 to 450 cps, 1000 to 5000 lines/min, and 4 to 800 pages/min.
	Language scripts: Printers must be capable of producing output in different languages familiar to different groups of users. The printers are available in almost all scripts (e.g., English, Japanese, etc.), and thus are classified on the basis of scripts (also called fonts).
	Colour: Printers may be capable of producing output in a single colour, in two or three colours, or in multiple colours. The printers capable of printing in single or two or three colours are suitable for producing textual documents while printers capable of printing in multiple colours are suitable for producing multiple-colour graphic outputs. Thus, it is always desirable to have printers that can print in multiple colours.

15.  Discuss the various impact printers.

Ans.: The various impact printers are dot matrix printer, daisy wheel printer, and drum printer.

Dot Matrix Printer

Dot matrix printer (also known as wire matrix printer) uses the oldest printing technology and it prints one character at a time. It prints characters and images as pattern of dots. The speed of dot matrix printers is measured in characters per second (cps). Most dot matrix printers offer different speeds depending on the quality of print desired. The speed can vary from about 200 to over 500 cps. The print quality is determined by the number of pins (the mechanisms that print the dots), which can vary from 9 to 24. The more pins per inch, the higher the print resolution. The best dot matrix printers (24 pins) can produce near letter-quality type image. Most dot matrix printers have a resolution ranging from 72 to 360 dpi.

Dot matrix printer is inexpensive and has low operating costs. It is able to use different types of fonts, different line densities, and different types of paper. Many dot matrix printers are bi-directional, that is, they can print the characters from either directions, left or right. The major limitation of dot matrix printer is that it prints only in black and white and the pattern of dots that make up each character are visible on the print produced by it, making it look unprofessional. In addition, as compared to printers like laser printers, it produces low to medium quality printing. The image printing ability is also very limited. It may not be able to print graphic objects adequately but can handle applications such as accounting, personnel, and payroll very well. It is commonly used in low-cost, low-quality applications like cash registers. It is limited to situations where carbon copies are needed and the quality is not too important.

Daisy Wheel Printer

If one requires a printer that can produce professional letter-quality documents, then a daisy wheel printer is needed. 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. It is commonly referred to as letter-quality printer as the print quality is as good as that of a high-quality typewriter.

Daisy wheel printer produces high-resolution output and is more reliable than dot matrix printer. It can have speed up to 90 cps. It is also called smart printers because of its bi-directional printing and built-in microprocessor control features. However, it gives only alphanumeric output. It cannot print graphics and cannot change fonts unless the print wheel is physically replaced. It is usually very slow because of the time required to rotate the print wheel for each character desired. It is slower and more expensive than dot matrix printer. However, if the appearance of the correspondence is important and graphics is not required, a daisy wheel printer is a better choice.

Drum Printer

It is also called line printer as it can print a line in a single operation. Generally, it is used because of its speed as it uses special tractor-fed paper with pre-punched holes along each side. This arrangement allows a continuous high-speed printing. Its printing speed varies from 300 to 2000 lines/min with 96 to 160 characters on a 15-inch line. Although such printers are much faster than character printers (such as dot matrix and daisy wheel printers), it tends to be quite loud, has limited multi-font capability, and often produces lower print quality than most recent printing technologies. It is designed for heavy printing applications. For example, in businesses where enormous amounts of materials are printed, the low speed character printers are very slow; therefore, the users need high-speed line printers. Although, it has high speed of printing, it is very expensive and its character fonts cannot be changed. Moreover, the strike of the hammer should be precise. A single mistimed strike of the hammer may lead to wavy and slightly blurred printing.

16.  Name the printer that is commonly used in homes. Give its advantages along with its working.

Ans.: The most common type of printer found in homes is the ink-jet printer. An ink-jet printer is a printer that places extremely small droplets of ink onto paper to create an image. Being a non-impact printer, it does not touch the paper while creating an image. Instead, it uses a series of nozzles to spray drops of ink directly onto the paper. It was originally manufactured to print in monochrome (black and white) only. However, the print head has now been expanded and the nozzles increased to accommodate cyan (C), magenta (M), yellow (Y), and black (K). This combination of colours is called CMYK. It allows for printing images with nearly the same quality as a photo development lab using certain types of coated paper. This printer can print any shape of character, which a user can specify as it produces printed output as pattern of tiny dots. This allows the printer to print many special characters, different sizes of print, and enables it to print graphics such as charts and graphs. It typically print with a resolution of 600 dpi or more. Due to the high resolution, it produces high-quality graphics and text printouts. It is also affordable, which appeals to small businesses and home offices. It prints documents at a medium pace but slows down if printing a document with multicolours. This printer can print about 6 pages/min and can be programmed to print symbols such as Japanese or Chinese characters.

Working of Ink-jet Printer

An ink-jet printer places extremely small droplets of ink onto the paper to create a character or an image. It has a print cartridge with a small series of electrically heated chambers. These chambers are attached to 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, the software gives instructions regarding the type and the quantity of colours. It also tells the position where the dots of ink should be sprayed. There are two main ways to drop the ink droplets: bubble-jet and piezo-electric technologies. Bubble-jet technology uses heat to fire ink onto the paper. There are three main stages with this method:

1. The squirt is initiated by heating the ink to create a bubble until the pressure forces it to burst and hit the paper.
2. The bubble then collapses as the element cools.
3. The resulting vacuum draws ink from the reservoir to replace the ink that was ejected.

Piezo-electric technology uses a piezo crystal at the back of the ink reservoir. It flexes when an electric current flows through it. Therefore, whenever a dot is required, a current is applied to the piezo element, the element contracts and in doing so forces a drop of ink out of the nozzle.

17.  Explain a laser printer and its working concept in detail.

Ans.: A laser printer provides the highest quality text and images for personal computers today. It is a very fast printer, which operates on the same principle as that of a photocopy machine. Most laser printers can print text and graphics with a very high quality resolution. It is also known as page printers because it processes and stores the entire page before it actually prints it. It produces sharp, crisp images of both text and graphics, providing resolutions from 300 to 2400 dpi. Today, the resolution of most printers is 600 dpi. It is quiet and fast, able to print 4–32 text-only pages/min for individual microcomputers and up to 200 pages/min for mainframes. It can print in excess of 2000 lines/min. Furthermore, it can print in different fonts, that is, type styles and sizes. It is often faster than ink-jet printers but is more expensive to buy and maintain than the other printers. The cost of this printer depends on a combination of costs of paper, toner replacement, and drum replacement. It is useful for volume printing because of its speed.

Working of Laser Printer

The core component of laser printing system is the photoconductive drum. A rotating mirror inside the printer causes the beam of a laser to sweep across the photoconductive drum. Initially, the beam of laser charges the photoconductive drum positively. When the charged photoconductor is exposed to an optical image through a beam of light to discharge, a latent or invisible image is formed. At the point where the laser strikes the surface of drum, it creates a dot of positive charge. These points are represented by a black dot, which will be printed on the paper. After this, the printer coats the drum with a container that contains a black powder called toner. This toner is negatively charged, and so it clings to the positive areas of the drum surface. When the powder pattern gets fixed, the 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. Since the paper is moving at the same speed as the drum, the paper picks up the image pattern precisely. Finally, the printer passes the paper through the fuser, a pair of heated rollers. As the paper passes through these rollers, the loose toner powder gets melted and fuses with the fibres in the paper. The paper is then brought out of the printer. Figure 4.3 illustrates the working of laser printer.

Figure 4.3 Working of a Laser Printer

18.  Write a short note on HYDRA printer.

Ans.: 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. Apart from these devices, some HYDRA printers contain memory card slots that facilitate easier printing of photos and also have the in-built wireless capabilities that make sharing of this printer with other systems easier. It is useful for small organizations due to its small size, less space requirement, and cost effectiveness. The cost of this printer depend on the technology (ink-jet or laser) being used. It saves power to a great extent as only one power outlet is required for performing various operations. It is easy to install and maintain and has easy-to-use GUI (graphical user interface) that helps the user to understand its functions easily.

19.  Describe the application areas where plotters are useful. Discuss the various types of plotters.

Ans.: A plotter is a pen-based output device that is attached to a computer for making vector graphics, that is, images created by a series of many straight lines. It is used to draw high-resolution charts, graphs, blueprints, maps, circuit diagrams, and other line-based diagrams. It is similar to printer, but it draws lines using a pen. As a result, it can produce continuous lines, whereas printer can only simulate lines by printing a closely spaced series of dots. Multicolour plotter uses different-coloured pens to draw different colours. Colour plots can be made by using four pens (cyan, magenta, yellow, and black) and need no human intervention to change them.

Being vector-based, a plotter tends to draw much crisper lines and graphics. The lines drawn by this device are continuous and very accurate. However, the plotter is considered a very slow output device because it requires excessive mechanical movement to plot. Furthermore, it is unable to produce solid fills and shading. It is relatively expensive as compared to printers but can produce more printouts than standard printers. It is mainly used for CAD and CAM applications such as printing out plans for houses or car parts. It is also used with programs like AutoCAD (computer-assisted drafting) to give graphic outputs. There are two types of plotters:

1. Drum plotter: In drum plotter, the paper on which the design is to be printed is placed over a drum. It consists of one or more pen(s) that are mounted on a carriage that is horizontally placed across the drum. The drum can rotate in either clockwise or anti-clockwise direction under the control of plotting instructions sent by the computer. In case, a horizontal line is to be drawn, the horizontal movement of a pen is combined with the vertical movement of a page via the drum. The curves can also be drawn by creating a sequence of very short straight lines. In this plotter, each pen can have ink of different colours to produce multicolour designs. It is used to produce continuous output such as plotting earthquake activity or for long graphic output such as tall building structures.
2. Flatbed Plotter: It consists of a stationary horizontal plotting surface on which paper is fixed. The pen is mounted on a carriage that can move horizontally, vertically, leftwards, or rightwards to draw lines. In this plotter, the paper does not move, the pen-holding mechanism provides all the motion. It is instructed by the computer on the movement of pens in the xy coordinates on the page. It is capable of working on any standard, that is, from A4 size paper to some very big beds. Depending on the size of the flatbed surface, it is used in designing of ships, aircrafts, buildings, and so on. The major disadvantage of this plotter is that it is a slow output device and can take hours to complete a complex drawing.

20.  Write a short note on computer output microfilm (COM). Explain the process of creating microfilms.

Ans.: Computer output microfilm (COM) is an extremely high speed, low cost process that records computer-generated information directly from the computer tape or cartridge to a miniaturized microfilm media. The microfilm product is in fiche or roll format, which can be duplicated rapidly and inexpensively. This process can produce data in microfilm form at a highly significant speed from that of a paper printer. The image area of the copy is dramatically reduced, up to 1/40 of its original size; yet, it retains its original clarity.

COM results in material, space, and equipment savings along with mailing costs and information retrieval savings. In addition, hard copy prints can be made without loss of detail, when compared with the original document. It facilitates indexing to access information. Furthermore, it provides an inexpensive way to preserve records from a variety of electronic sources. Such records might need to be stored for long periods and referenced only occasionally. The main disadvantage, however, is that it is expensive to install COM and microfilms cannot be read without the assistance of a special reader device.

Generally, a COM system is ideal for applications where there is a large amount of information to be retained and therefore very useful for manuals, industrial catalogues, and archives. Microfilm output is used for the distribution of airline schedules, medical X-rays, and list of books in print. Banking and insurance companies, government agencies, public utilities, and many other types of organizations are regular users of COM.

To retrieve the images, the microfilm images may be enlarged on a viewing screen with the help of a microfilm reader for comfortable reading. Microfilms can be created in the following two ways:

1. Photographic process: It is the oldest method of creating microfilms. Essentially, it is a form of miniature photography that uses a microfilm camera for producing microfilms. When the original documents are fed through a microfilm camera, it captures the document into a reduced-size photo. Once all the photographs are taken, the 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: In this process, the user can entirely avoid the film developing process. This process uses a monitor and the computer output is read onto the magnetic tape. After this, data are printed on the microfilm by using a microfilm recorder. Moreover, it is possible to couple a microfilm machine directly to a computer; therefore, the recorder can directly receive information from the computer. As the recorder projects the computer information onto the screen, a high-speed camera photographs the displayed information. The process of creating microfilm from magnetic tape is illustrated in Figure 4.4.

Figure 4.4 Creating Microfilms from Magnetic Tape: COM, Computer Output Microfilm

21.  What is the role of a visual display unit? Also discuss the types of monitors.

Ans.: The monitor (also known as visual display unit) is the most frequently used output device for producing soft-copy output. 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 either be a monochrome display or a colour display. A monochrome screen uses only one colour (usually white, green, amber, or black) to display text on contrasting background. A colour screen commonly displays 256 colours at one time from a selection of over 256,000 choices. Monitors are available in various sizes like 14, 15, 17, 19, and 21 inches. The size of the display is described based on two parameters: aspect ratio and screen size. Aspect ratio is the ratio of the width of the display screen to the height, that is, the ratio of vertical points to the horizontal points necessary to produce equal-length lines in both directions on the screen. Generally, computer displays have an aspect ratio of 4:3. Like televisions, screen size is normally measured diagonally (in inches), the distance from one corner to the opposite corner. The description of various types of monitors is as follows:

	Cathode ray tube (CRT): Nowadays, most computer monitors are based on cathode ray tube (CRT) technology. The basic operation of this tube is similar to that in television sets. The primary components in a CRT are the heated metal cathode and a control grid. Heat is supplied to the cathode by directing a current through a coil of wire, called the filament, inside the cylindrical cathode structure. This causes electrons to be boiled off the hot cathode surface. In the vacuum inside the CRT envelope, the free, negatively charged electrons are then accelerated towards the phosphor coating by a highly positive voltage. The accelerating voltage can be generated with a positively charged metal coating on the inside of the CRT envelope near the phosphor screen, or an accelerating anode can be used.
	Liquid crystal display (LCD): With the widespread use of smaller computers like PDAs and laptops, a new type of display liquid crystal display (LCD) has made a big impact on the computer market. LCD screens have been used since long in notebook computers but are also becoming popular as a desktop monitor. The term ‘liquid crystal’ sounds like a contradiction. We generally conceive a crystal as a solid material like quartz and a liquid as water like fluid. However, some substances can exist in an odd state that is semi-liquid and semi-solid. When they are in this state, their molecules tend to maintain their orientation like the molecules in a solid, but move around to different positions like the molecules in a liquid. Thus, liquid crystals are neither a solid nor a liquid. Manufacturers use this amazing ability of liquid crystals to display images.
	Plasma display: It is also known as thin-panel. It is constructed by filling a gas (neon or xenon) between the two glass plates. One glass plate consists of vertical conductors and the other consists of horizontal conductors. When the voltage is applied to the pair of horizontal and vertical conductors, the gas at the intersection of two conductors glows. The advantage of plasma display is that it has the capability of producing more than 16 million colours and is lighter and less bulky than CRT. However, it is heavier than LCD display and requires more power.
	Thin-film electroluminescent display: This display is similar to the plasma display except the fact that the space between the glass plates is filled with phosphorescent substance (usually zinc sulphide doped with manganese) instead of gas. When high voltage is applied to the crossing conductors, the phosphoric substance at the intersection of two conductors becomes conductor and generates the electrical energy. This energy is absorbed by the manganese atoms and then released as a spot of light. The main problem with thin-film electroluminescent display is that it requires more power.

22.  Differentiate between LCD and CRT monitors.

Ans.: Although both the LCD and CRT monitors are most frequently used types of displays in computers, they are worlds apart in terms of what is important when making a purchase decision. Table 4.1 lists the differences between these two monitors.

Table 4.1 Differences Between LCD and CRT Monitors

On the basis of	LCD	CRT
Size	It is lightweight and compact.	It is non-compact and heavier.
Resolution	It is designed to work in a single resolution.	It is designed to work for many resolutions.
Brightness	It produces high brightness with its florescent backlight.	It produces less brightness.
Power consumption	It consumes less power.	It consumes more power.
Refresh rate	It has slower refresh rate, usually about 60 Hz.	It has faster refresh rate, usually about 85 Hz.
Pixel response time	It has quite slow response time.	It has extremely fast response time.
Viewing angle	It is best viewed from head on.	It can be viewed at almost any angle.
Viewing area	It has same viewable area as its advertized area.	Its viewing area is less than its advertized area. For example, 19-inch. CRT monitors have 18 inch of viewable area.
Cost	It is cheap.	It is costly.

23.  What is a voice response system? How does it function? Give some of its typical applications.

Ans.: Voice response system has an audio-response device that produces audio outputs. These sounds are pre-recorded in a computer system. Each sound has a unique code. Whenever an enquiry is sought from the system, the computer responds in digital form which is sent to voice devices that unscramble the digital information and produces sound messages to the requesting computer.

There are two basic approaches to get a computer to talk to the user. The first is synthesis by analysis, in which the device analyzes the input of an actual human voice speaking words, stores, processes the spoken sounds, and reproduces them as needed. The process of storing words is similar to the digitizing process. In essence, synthesis by analysis uses the computer as a digital tape recorder. The second approach to synthesizing speech is synthesis by rule, in which the device applies a complex set of linguistic rules to create artificial speech. Synthesis based on the human voice has the advantage of sounding more natural but is limited to the number of words stored in the computer. The standard computer system can provide audio output with the addition of two components: a speech synthesizer that does the speaking and a screen reading software that tells the synthesizer what to say. The synthesizer can be a computer card inserted into the computer or software that works with the computer's sound card. Screen reader is a software program that allows the user to control the synthesizer so that he can access text, which is displayed on the computer monitor, with combinations of keystrokes. Some screen review software use the standard computer keyboard keys, some use the numeric keypad, and some use special external keypads. A visually impaired user can use a screen reader to read anything on the screen. The screen reading software can even notify a user about various computer messages that ‘pops up’ on the monitor from time to time.

Voice output has become common in many places like airlines, bus terminals, banks, and brokerage houses. It is typically used when an inquiry is followed by a short reply (such as a bank balance or flight time). Many businesses have found other creative uses for voice output. For example, automatic telephone voices take surveys, inform customers that catalog orders are ready to be picked up, and perhaps remind consumers that they have not paid their bills. Moreover, people with a total or partial speech handicap face the problem of communicating their wishes and needs to others. Speech output systems are a valuable aid in this case.

24.  Why projectors are needed? Discuss two types of projectors.

Ans.: Projector (also called screen image projector) is an output device that is used to project information from a computer on to a large screen, so that it can be simultaneously viewed by a large group of people. Projection display is commonly used for classrooms training or conference room or for multimedia presentations with a large audience. Like monitors, projector provides a temporary, soft-copy output. Projector is of the following two types:

1. LCD projector: LCD is the acronym for liquid crystal display. It is the established technology used by most of the leading manufacturers. Most of today's LCD projectors contain three separate LCD glass panels, one each for red, green, and blue components of the image signal being fed into the projector. As light passes through the LCD panels, individual pixels can be opened to allow light to pass, or closed to block the light. This activity modulates the light and produces the image that is projected onto the screen.
2. DLP projector: DLP is the acronym for digital light processing. It is a proprietary technology developed by Texas Instruments. It uses a single DMD (digital micromirror device) chip that has thousands of tiny mirrors, each representing a single pixel. These mirrors tilt back and forth, directing the light either into the lens path to turn the pixel ON, or away from the lens path to turn it OFF and create the image. It is a newer technology than LCD and is used on some of the smallest, lightest projectors currently available. It handles video images extremely well.

25.  Write a short note on electronic whiteboard.

Ans.: Electronic whiteboard is an interactive presentation device that works electronically to display digital images, drawings, and text in different colours. It is generally mounted on the wall and is connected to a computer (through USB, serial port, or wireless technology like Bluetooth) and projector. The projector projects the computer's desktop on the whiteboard and the user can interact with it using electromagnetic pens, fingers, or other pointing devices. The electromagnetic pens can be configured to any colour or width.

User can activate programs, applications, and menus as well as can enter text using either on-screen keyboard or handwriting recognition utility. Nowadays, most whiteboards come with software that provides various tools and features to create virtual versions of paper flipcharts with pen, highlighter, etc., enhancing the use of electronic whiteboard to a great extent. It is widely used for various purposes such as to display presentations, for teaching in classrooms, in corporate meetings, and professional sports coaching. An interactive electronic whiteboard can be classified into one of the following categories:

	Touch-based whiteboard: It allows user to use their fingers or other pointing devices to interact with it. The working on this whiteboard is easy as anything can be used as a pointer, for example, a stick, finger, etc., where touch of a finger on the whiteboard is considered as a left click of the mouse.
	Pen-based whiteboard: It mainly uses an electromagnetic pen that alters electrical signals produced by the board and does not require batteries or power source for its operation. When the tip of the pen is pressed to the whiteboard, it results in the activation of switch in the pen, which signifies mouse click to the computer. It is widely used by professional digital artists and designers as they help in providing more accurate information.
	Wii remote, IR pen-based whiteboard: It works on sound electronic and optical principles. It uses Wii remote control with IR camera placed in front of the remote control to track dots of an IR light that is created by the IR pen. It has become much popular due to its portability and reduced cost.

26.  How is a headphone different from a headset?

Ans.: Headphone is an audio device equipped with a pair of speakers that are attached to a headstrap worn by the users. It is used with almost all electronic devices such as portable computers, CD/DVD players, mp3 player, and iPod. It comprises high-quality speakers, is lightweight, and is very comfortable to wear. It can be easily connected to a computer via a mini-stereo plug. It allows the users to only listen; however, some applications like live chats, videoconferencing, and telecalling services demand the user to also speak at the same time. For such applications, headset is used instead of headphone.

A headset is a combination of one or two speakers and a microphone with both the speaker and the microphone attached to a headstrap. The speaker(s) allows the person to hear the conversation and the microphone allows the user to communicate with the person on the other end.

27.  What is a computer terminal? Discuss the area where VDTs can be employed.

Ans.: Computer terminal is a special unit that can perform both input and output. A terminal is an input/output device that uses a keyboard for input and a monitor for output. Due to this reason, a terminal is also known as a video display terminal (VDT). It can be categorized into the following three types:

1. Dumb terminal: It refers to a terminal that has no processing or programming capabilities. It is designed to communicate exclusively with a host computer. Usually, it consists of a screen and a keyboard used to access a host computer. It has electronics circuitry enough to interpret incoming instructions from the host computer, to display characters on the screen, to interpret keystrokes on the keyboard, and to pass them on to the host computer. Generally, it is used for simple data entry or retrieval tasks. An example of a dumb terminal is one used by airline clerks at airport ticket and check-in counters.
2. Smart terminal: This terminal has built-in processing capability and memory but does not have its own storage capacity. In comparison to the dumb terminal, smart terminal can communicate and retrieve the data and can perform a limited processing of its own, that is, editing or verification of the data. However, this kind of terminal cannot be used for programming. It is often found in local area networks in offices.
3. Intelligent terminal: It has memory and inbuilt microprocessors. It is also known as user-programmable terminal. This terminal can independently perform a certain number of jobs without even interacting with the mainframe. Although it is an intelligent terminal, some workstations are designed without disk drives. Due to this, the restricted data cannot be downloaded or copied.

28.  List the devices that can be used as input as well as output devices.

Ans.: The examples of the devices that can be used as input as well as output devices are touch screen, digital camera, CD, and storage devices like hard drive.

Multiple-choice Questions

1.  _________ is the most commonly used input device.

(a) Keyboard

(b) Mouse

(c) Joystick

(d) Scanner

2.  Mouse, trackball, and joystick are the examples of _________.

(a) Scanning devices

(b) Storing devices

(c) Pointing devices

(d) Multimedia devices

3.  Choose the most suitable device among the following for playing computer games.

(a) Handheld scanner

(b) Joystick

(c) Optical mark reader

(d) Digital camera

4.  Light pen is frequently used in _________.

(a) Computer-aided design

(b) Word processing

(c) Presentation

(d) Spreadsheet

5.  Which of the following technique is best suited for bank cheques?

(a) OCR

(b) OMR

(c) BAR

(d) MICR

6.  Which of the following is not an output device?

(a) Printer

(b) Keyboard

(c) Monitor

(d) Plotter

7.  The _________ is also called as letter-quality printer.

(a) Dot matrix printer

(b) Ink-jet printer

(c) Daisy wheel printer

(d) Laser printer

8.  LCD stands for _________.

(a) Liquid colour display

(b) Light colour display

(c) Lithium crystal display

(d) Liquid crystal display

9.  Which of the following is not a computer terminal?

(a) Intelligent

(b) Smart

(c) Both (a) and (b)

(d) None of these

10.  The _________ terminal is referred as non-programmable terminal.

(a) Dumb

(b) Smart

(c) Intelligent

(d) None of these

Answers

1. (a)

2. (c)

3. (b)

4. (a)

5. (d)

6. (b)

7. (c)

8. (d)

9. (d)

10. (a)