Fundamentals Of Computer- Chapter-3- INPUT & OUTPUT DEVICES

INPUT & OUTPUT DEVICES

    Input devices are used to feed data and instruction to the computer. The result produced by the CPU s in the form of electronic binary signals It has to be converted to a form, which can be understood by human beings This function is performed by Output Units.

1. Input Devices

These are the various input devices.

1.1 Keyboard

        Keyboard is one of the primary means by which we communicate with the computer. There are many different types of computer keyboards: wired, wireless, ergonomic, and multimedia. Although there may be differences in the location of some keys or features, keyboards are very similar and allow you to accomplish basically the same tasks. A typical PC keyboard is shown in the figure below.

        The computer keyboard very similar to typewriter keyboard, with the addition of special keys including numeric keypad, navigation and editing keys, directional keys, function keys, and the escape key (ESC). Special function modifier keys specific to Windows include the control key (CTRL), the alternate key (ALT), and the Windows key. The layout of these keys is derived from the original layout of keys on a typewriter. The most widely used layout in the English language is called QWERTY, named after the sequence of the first six letters from the Settle There are actually three different PC keyboard: the original PC keyboard, with a keys kythe AT keyboard, also with 84 keys and the enhanced keyboard, with 101 keys. The keys on your keyboard can be divided into several groups based on function. They are;

(a) Character/Typing (alphanumeric) keys:
      These keys include the same letter, number, punctuation, and symbol keys found on atraditional typewriter.

(b) Control/Special keys:
     These keys are used alone or in combination with other keys to perform certain actions. The most frequently used control keys are Ctrl, Alt, the Windows logo key Picture of the Windows logo key, and Esc.

(c) Function keys:
    The function keys are used to perform specific tasks. They are labeled as F1, F2, F3, and so on, up to F12. The functionality of these keys differs from program to program.

(d) Directional & Navigation keys:
          These keys are used for moving around in
documents or webpages and editing text. They include the arrow keys, Home, End, Page Up, Page Down, Delete, and Insert.

(e) Numeric keypad:
        The numeric keypad is handy for entering numbers quickly. The keys are grouped together in a block like a conventional calculator or adding machine.

(f) Escape Key:
      The Escape (Esc) key allows you to stop a function or action. For example, if a webpage is taking a long time to load, you can press the Escape key to stop loading it.

1.2 Mouse

     A Mouse is also called a pointing device' because it enables you to control what happens on the screen by moving the mouse on your desk and pointing, clicking and selecting items on the screen.

      A Mouse usually has two buttons, a right and left one and also a central wheel which allows you to scroll up and down the page (some mice have upto five buttons). The left and right button have different functions. Left clicking usually lets you put your cursor at a certain point on the page or lets you choose a menu item. Right clicking brings you up a list of relevant menu items from which you can select a task. Many of the older styles of mice used a ball which moved against two internal rollers to record the direction that the mouse was being moved in. Recent versions of mice used optical or Wireless technology to track mouse movement.

Mouse alternatives

         There are other devices that can do the same thing as a mouse but that have a different look and feel. Many people find them to be easier to use, and they also require less disk space thanamouse. The most common mouse alternatives include:

1.2.1 Trackball:

         A trackball has a ball on top that can rotate freely. Instead of moving the device like a mouse, you can roll the ball with your fingers to move the pointer Some mobile devices have miniature trackballs that can be controlled with your thumb.

1.2.2 Touchpad:

     A touchpad also called trackpad-is a touch-sensitive pad that lets you control the pointer by making a drawing motion with your finger. Touchpads are common on laptop computers.

1.3 Joystick:

        Joysticks were originally used by pilots as part of an airplane controls and the technology was developed to let computer gamers experience a more realistic game environment.You can move joysticks in many directions and the joystick tells the computer which direction it has been moved into. They also have one or more buttons whose position when pressed can be read by the computer. Joysticks can also be used for controlling machines such as cranes, trucks and powered wheelchairs.

1.4 Touch screen

         A Touch screen is the only device which works as both an input and an output device. YOU view the options available to you on the screen (output) and you then use your finger to touch the option that you have chosen (input). Touch screens work particularly well with a menu driven interface. For example, a cashpoint (ATM) at a bank would first of all ask which service you want. You touch the option 'withdraw cash' on the screen. You are then presented with another choice how much cash do you want to withdraw?' Once you have chosen how much you then get other options such as 'do you want a receipt?'. Another major use of touch screens are on smart phones and modern tablet computers. Each 'app is accessed by an icon on the touch screen.

1.5 Graphics Tablet

           Graphics tablets are often used by graphics designers and illustrators. By using a graphics tablet a designer can produce much more accurate drawings on the screen than they could with a mouse or other pointing device. A graphics tablet consists of a flat pad (the tablet) on which you 'draw with a special pen.As you draw on the pad an image is created on the computer monitor from within the application that the tablet is connected to

1.6 Scanner

           Scanners can be used to convert images or text on paper into a digital format that can be used by the computer. A scanner works by shining a beam of light onto the surface of the object that you are scanning. This light is then reflected back onto a sensor that detects the colour of the light. This is then used to build up the digital image. Items that are scanned are usually stored in an image format. However, special software.

       The following are some of the common types of scanners:

1.6.1 Optical Character Recognition

        Optical Character Recognitioncan be used to convert text on the paper into text which can be edited with a word processor.

1.6.2 Barcode Reader:

       A barcode reader is an automatic input device which is used to scan or 'read' the barcode by using a visible red light. The reflected light is translated into digital data that is interpreted by the computer to identify the product and price from the database. Barcode readers are commonly used in supermarkets and big retail stores at sale counters. As these scanners are normally held in hand, they are called handheld scanners.

1.6.3 Magnetic Stripe Reader :

        Magnetic strips are usually found of the back of most credit cards, cheque guarantee card, loyalty cards, membership cards etc. The magnetic strip can hold personal details such as account number and name. To read the data on the card, it is 'swiped through a Magnetic Stripe Reader machine and the data is read and fed back to the computer.

1.6.4 Optical Mark Reader :

      Optical Mark Reader (OMR) Have you ever looked closely at the National LOTTERY TICKET selection form? Or have you ever had to do a multiple choice test at school where you had to use a pen to show your answer. These forms are scanned by a special piece of equipment called an 'Optical Mark Reader (OMR). They detect the presence of your pencil mark by reflecting light into it. Less light is reflected where a mark has been made. The OMR then interprets the pattern of marks and sends the results to the computer for storage, analysis and reporting.

1.7 Microphone

        A microphone can be used to input sound. The sound is detected by the microphone and an electrical signal is transmitted to the computer. Special hardware is used to convert this analogue data into digital data so it can be stored and manipulated. In the last few years a number of voice recognition systems have been developed. These packages let the user dictate the text into a computer and then convert the speech to text.

1.8 Webcam

          A webcam is short for web camera, A webcam is an input device because it captures a video image of the scene in front of it It is either built into the computer (e.g.laptop) or it is connected through an USB cable. Webcams are commonly used to allow people to see each otherwhile chatting over the internet. Formally this is called teleconferencing

1.9 Biometric Devices

          There is an increasing trend towards using biometric data from people in order to identify them.Fingerprint and retinal identification are being used in many places now and even facial recognition systems are starting to be introduced. Special devices are needed to capture the biometric data which is then passed onto the computer for processing and identification. A common use of biometric data is inside the modern UK passport. A microchip is included in the passport that contains the electronic data unique to the person. At passport control, a biometric reader is used to confirm identity.

2 OUTPUT DEVICES

         The result produced by the CPU is in the form of electronic binary signals. It Has to be converted to a form, which can be understood by humans. This function is performed by Output Unit Below we discuss the various output devices used in computer.

2.1 Monitor

    The monitor works with a video card, located inside the computer case, to display images and text on the screen. Newer monitors usually have LCD (liquid crystal display) or LED (light-emitting diode) displays. These can be made very thin, and they are often called flat-panel displays. Older monitors use CRT (cathode ray tube) display, CRT monitors are much larger and heavier, and they take up more desk space. LED displays are actually LCDs that are backlit with light- emitting diodes. This allows for greater contrast than a traditional LCD.
       Monitors are available in various sizes ranging from 8 inches to 50 inches. Some monitors have built-in TV tuner and can also work as a TV. The amount and quality of information you can see on a monitor depends on its dot pitch, pixel (pictureelement) and the video adapter card used in PC. Since 2000, most computer monitor are SVGA (Super Video Graphics Array) color or better. The SVGA monitor has a resolution of 800 pixels by 600 rows, commonly referred to by 800 x 600 and displays up to 16 colors. These days most monitors can display thousands of colors and have a resolution of 1024x768 or higher. A higher resolution monitor is recommended for
graphic applications.

2.2 Printer

         The printer is an output device that is usedt o print documents on paper. Various kinds of printers are used with PCs. A few years ago, the Dot Matrix Printer (DMP) was the most commonly used printer with PCs because of its low cost and reasonably good speed. The print head in a DMP contains a few tiny needles. There are 7 or 9 needles in a low quality DMP and up to 24 needles in a high quality DMP. At the time of printing, as the head moves from one end of the paper to the other, these needles are fired selectively to print different characters of graphic, Dot Matrix Printers usually have a printing speed of 100 to 500 characters per second.

2.2.1 Inkjet Printer

     Nowadays, Inkjet/Bubble Jet printers are also the popular choice for use with PCs. These printers offer good print quality and noiseless operation. These are non-impact printers that print characters and graphics by spraying very tiny drops of ink directly onto paper. The print quality of these printers is much better compared to DMPs. The typical print quality of these printers is from 300 dots per inch (DPI) to 4800 DPI. Most of these printers can also print in color. An inkjet printer is shown in the figure below.

2.2.2 Laser printer

       Laser printers are also being commonly used with high-end PCs; particularly those used for Desktop Publishing (DTP). They provide very high quality printout, typically in the range of 300 DPI to 2400 DPI; however, these are costlier than DMP and Inkjet printers. The typical printing speed of laser printers is between 3 to 30 pages per minute. It produces good quality images by the same technology that photocopiers use. High-end laser printers can also print in color. A laser printer is shown in the following figure.

2.2.3 Multi-Function Printers

         Multi-function printers can perform other jobs besides printing. For instance, a multi function printer may include a scanner. By printing the scanned document, the printer can act as a copier. Faxing capability is another useful function available in some of the multi-function printers. The printer may include a dial pad to enable the user to send the fax. Of course, the printer can easily print the received faxes since it already has the printing capability. A multi-function printer is shown in Figure below, that can copy, scan and fax.
     Line printers, drum printer and chain printers are some other types of impact printers. These printers are high-speed printers that can print up to 6000 lines per minute, These printers are generally used with mini or mainframe computers, and are not as popular with PCs.

2.3 Plotter

     Plotter Is a printer that interprets commands from a computer to make line drawings on paper with one or more automated pens. Unlike aregular printer, to plotter can draw continuous point-to-point lines directly from vector graphics files or commands. There are a number of different types of Plotters: a drum plotter draws on paper wrapped around a drum which tums to produce one direction of the plot, while the pens move to provide the other direction; a flatbed plotter draws on paper placed on a flat surface; and an electrostatic plotter draws on negatively charged paper with positively charged toner.

        Plotters were the first type of printer that could print with colorand render graphics and full size engineering drawings. Asarle plotters are much more expensive than printers. They are most frequently used for CAE (computer- aided engineering) applications, such as CAD (computer-aided design) and CAM (computer-aided manufacturing). Hewlett Packard (HP) is the leading vendor of plotters worldwide.

2.4 Projector

            A projector is a device that uses light and lenses to take computer output and project a magnified image onto a larger screen or wall. It is widely used in classrooms and auditoriums for instruction and slide presentation. Projectors can magnify still or moving images depending on how they are built.

    There are two main types of digital projection display systems. The older, less expensive type employs three transparent liquid-crystal display (LCD) panels, one for each of the primary colors (red, green, and blue). The light transmittivity of each pixel varies depending on the image data received from the computer.
      A newer, more expensive scheme is known as Digital Light Processing (DLP), aproprietary technology developed by Texas Instruments. In a DLP display, tiny mirrors are used instead of transparent panels. Each mirror represents one pixel. Advantages of DLP technology include light weight, high contrast, and lack of pixelation.
        The Third type of projection LED projector, is named for the light source, not the type of projection technology.