Computer Systems: Keyboards, Readers, Monitors, Printers, and Peripherals, Study notes of Voice

Download Computer Systems: Keyboards, Readers, Monitors, Printers, and Peripherals and more Study notes Voice in PDF only on Docsity! Input and Output Devices 71 Unit 4: Input and Output Devices Introduction The unit 4 presents the information of input and output devices. A number of input/output devices are used with many types of microcomputers. Many of these are less complex versions of I/O devices that have been available for larger computer systems. The principal difference is that because they are intended for use with microcomputers, they are significantly slower and substantially cheaper. Few of these devices are discussed in this unit. Lesson 1: Input Devices 1.1 Learning Objectives On completion of this lesson you will be able to: • understand the functions of input devices • know different types of input devices. 1.2 Keyboards The most common of all input devices is the keyboard. Several versions of keyboards are available. The best and most expensive of these is the full-stroke keyboard. This is ideal for word processing and other volume data and program entry activities. This type of keyboard is available with most mainframe computer terminals or the expensive microcomputer systems. Some popular microcomputers offer enhanced keyboard for easy entry of numbers. This is accomplished with a smaller group of keys known as a numeric keypad at the right of the keyboard. These keys generally consist of the digits, a decimal point, a negative sign, and an ENTER key. This type of keyboard is ideal for accounting operations, which require a large volume of numbers to be entered. Keyboards generally utilize integrated circuits to perform essential functions, such as determining the combination of 1s and 0s, or binary code, to send to the CPU, corresponding to each key depressed, switching between shifted and nonshifted keys, repeating a key code if a key is held down for a prolonged period of time, and temporarily storing or "buffering" input when keys are typed too fast. Full-stroke keyboard, enhanced keyboard. Computer Basics 72 The keyboard arrangement provided as standard on most keyboards is the QWERTY arrangement, named for the six letters beginning the row at the top left of the keyboard (Figure 4.1). This arrangement was chosen intentionally to slow expert typists, since those who typed too fast would cause the keys on a mechanical typewriter to jam. Slowing down the typist was accomplished by scattering the most used around the keyboard, making frequently used combinations of letters awkward and slower to type. This QWERTY keyboard arrangement has been used for nearly a century. The Dvorak Simplified Keyboard (DSK) arrangement, designed in 1932 by August Dvorak, is the result of extensive ergonomic studies. Dvorak noted that with the QWERTY keyboard arrangement, typists used the weakest fourth and fifth fingers of their left hand a large proportion of the time. Thus, Dvorak rearranged the keyboard so that the five more frequently used vowels (a, o, e, u, and i) and the five most frequently used consonants (d, h, t, n, and s) were positioned on the home row where the fingers of the left and right hands rest, respectively (Figure 4.2). Thus, 70 percent of the typing is done on the home row. He then placed the next most frequently used characters in the row above the home row and the least frequently used characters in the row below the home row. This resulted in a reduction of finger movement of approximately 80 percent and overall, an increase in productivity of nearly 40 percent. Expert typists and word processors generally agree that using the Dvorak arrangement increases productivity while simultaneously decreasing fatigue. The world's fastest typing speed, nearly 200 words per minute, was achieved on a Dvorak keyboard. Despite these improvements the QWERTY keyboard arrangements is still the most common because of the difficulty of overcoming inertia and retraining. In the mean while, microcomputer manufacturers and software vendors are producing software that will convert your keyboard from QWERTY to Dvorak, and back again at will. To date, larger computer systems employ the traditional QWERTY arrangement only. QWERTY arrangement Dvorak simplified keyboard Input and Output Devices 75 -16 A B C D E -17 A B C D E -18 A B C D E -19 A B C D E -20 A B C D E -21 A B C D E -22 A B C D E -23 A B C D E -24 A B C D E -25 A B C D E -26 A B C D E -27 A B C D E -28 A B C D E -29 A B C D E -30 A B C D E -31 A B C D E -32 A B C D E -33 A B C D E Figure 4.3 Portion of a special-purpose optical mark form. Optical Mark Readers Optical mark readers (OMR) optically read marks on carefully printed forms. Optical mark forms are relatively expensive, as they must be printed with exact tolerances so that the marks will up under the optical sensing devices when read (Figure 4.3). The most popular use of such devices is optical character readers for scoring examinations in educational institutions. Optical Character Readers (OCR) Optical character recognition (OCR) devices can convert data from source documents to a machine-recognizable form. Current applications of optical scanning include billing, insurance premium notices, and charge sales invoices. At present, on OCR device can reliably read and interpret script or handwriting. However, some can read handwriting provided that certain general guidelines are observed when the data are written. Generally, optical character readers are limited with respect to hand-written characters and can only read handwritten digits and some symbols. Many OCR devices are available for the reading of typed characters, including digits, letters and some special characters. Not all printed characters can be read reliably on OCR readers. Generally, each reader is capable of reading only selected character styles. Even if the character style and spacing are acceptable, errors can result from reading a character that is not written perfectly. To reduce such errors, OCR devices generally compare the pattern read with the patterns to all acceptable character. The read character is assumed to be the Optical Mark Readers(OMR) Optical Character Recognition (OCR). Computer Basics 76 character whose stored pattern most closely matches the read pattern. This process is shown in Figure 4.4. A 18 Discrepancies C 10 Discrepancies D 0 Discrepancies Input and Output Devices 77 C 6 Discrepancies Figure 4.4: Character reads compare the digitized matrix of an unknown character against a stored set of templates. Because of the high cost of OCR devices, they are uneconomic unless a substantial number of documents are to be processed each day. CD, Web camera, disk drive, ATM, Scanner and bar code scanner can all be used as input devices. Pointing Systems Computer users frequently find it easier to point to something on a screen or at an item of text or graphical material they are entering into the computer, A number of devices are available to assist in fulfilling this need. Figure 4.5 : Various pointing input devices. Computer Basics 80 CD-ROM Pronounced see-dee-rom. Short for Compact Disc-Read-only Memory, a type of optical disk capable of shorting large amounts of data up to 1GB, although the most common size is 650 MB (megabyte). A single CD- ROM has the storage capacity to 700 floppy disks, enough memory to store about 300,000 text pages. CD-ROMs are stamped by the vendor, and once stamped, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. All CD-ROMs comform to a standard size and format, so you can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are capable of playing audio CDs, which share the same technology. CD-ROMs are particularly well-suited to information that requires large storage capacity. This includes large software applications that support color, graphics, sound, and especially video and are well suitable for tutoring, Figure 4.8 : A CD. Figure 4.9 : Composition of a CD. Input and Output Devices 81 1.4 Exercise 1. Multiple choice questions a. Increase in productivity using Dvorak simplified keyboard is nearly (i) 60 percent (ii) 30 percent (iii) 40 percent (iv) 50 percent. b. Which one is used for scoring examinations? (i) MICR (ii) OMR (iii) OCR (iv) none of them. c. Which one is used with video games for user input? (i) Touchscreen (ii) Mouse (iii) Digitize pad (iv) Joystick. d. Touchscreen is usually used to detect the touch of a (i) Human finger (ii) Pen (iii) Wooden stick (iv) none of them. 2. Questions for short answers a. Briefly describe the advantages of Dvorak simplified keyboard. b. What is the basic difference between OMR and OCR? c. What is a mouse in computer system? d. Write down the application of digitized pad and touchscreen. 3. Analytical questions a. Describe the keyboard as input device. b. Describe basic types of character readers. c. Describe different pointing systems. Computer Basics 82 Lesson 2: Output Devices 2.1 Learning Objectives On completion of this lesson you will be able to : • understand functions and characteristic of output devices • know different types of devices. 2.2 Monitors It is the most commonly used display device. The monitor, utilizes a cathode ray tube (CRT). CRT monitors generally produce images by the raster-scan method. In this method, an electron beam varying in intensity, is moved back and forth horizontally across the face of the monitor. As the beam is directed to each spot on the phosphor-coated screen, it illuminates the spot in proportion to the voltage applied to the beam. Each spot represents a picture element or pixel. When the electron beam has scanned the entire screen and illuminated each pixel, one can see a complete image. The image that can be seen is the one traced on the retinas of eyes by the light beam. However, this image will fade unless it is refreshed. Thus, the electron beam must scan the screen very rapidly (a minimum of 60 times per second), so that the intensity of the image remains approximately the same and the screen does not appear to flicker. The screen resolution of a particular monitor is determined by the number of pixels that make up the screen. Monitors are currently available with 64,000 to more than 2 million pixels per screen. The greater the resolution of a monitor the greater the storage demand on the computer. This is because the image must be stored in memory before it can be displayed. Two techniques used to store computer images are: bit-mapped and character-addressable. In a bit-mapped display, each pixel is uniquely addressable. Information must be stored for each pixel on the screen. This technique needs quite a large computer memory and provides the most detailed display. For graphical applications, such as CAD/CAM, this detail is essential. However, for applications such as word processing, a character- addressable display is appropriate. In a character addressable display, the screen is divided into character positions. Only the characters to be displayed are stored in memory. As each character is retrieved from memory, it is converted into a pattern of dots or pixels by a special character generator module. CRT monitors generally produce images by the rasterscan method. Input and Output Devices 85 others, a dot pattern can be created that gives the appearance of numbers, letters or special characters. Figure 4.10: Dotmatrix printers form characters with an array of dots. Here the letter A is shown printed by (a) a 9-pin printer, (b) a 24-pin printer. (c) a 9-pin letter-quality dot-matrix printer capable of overlapped dot printing. These extended wires are pressed against an inked ribbon to print the characters on the paper. Some slower and less expensive matrix printers (a) (b) (c) Dotmatrix Printers Computer Basics 86 print a character as a series of columns each one dot wide. It can be used to print special character shapes that can be used with graphics. For a typewriter-quality output, a special dot-matrix or daisy metal print element, similar in appearance to the arrangement of petals on a daisy flower. This element is rotated until the correct character is in position, and then pressed against an inked ribbon. The process is repeated for each character to be printed on a line. Typical for such printers range from 25 to 100 characters per second. Impact character printers are the common output devices used with personal and small business microcomputer systems. They are significantly cheaper than the line printers. Impact line printers, capable of printing a whole line at a time, employ print wheels or a moving chain or drum. The print-wheel printer consists of print wheels, each containing a full complement of digits and alphabetic characters in addition to a set of special characters. For printing, all print wheels rate positioned to represent the data to be printed on one line. They then impact simultaneously at a speed of about 150 lines per minute. Impact line printers and the chain and drum printers are commonly used. As the print chain or drum revives, each character is printed as it comes into position. Up to 150 characters per line can be printed at speeds of up to 2,500 lines per minute. Impact line printers are used almost exclusively to support larger computer systems. 2.5 Nonimpact Printers Nonimpact line printers, using laser, xerographic, electrostatic, or ink jet methods are the fastest printers. Before the development of the ink jet and laser printers, nonimpacts were not heavily used, for several reasons: • Special and more expensive paper was required. • Printed output was not as sharp or as clear as with impact printers. • Only a single-part form can be printed at a time. • Output could not be easily or satisfactorily copied on office copiers. Electrostatic and xerographic printers place a pattern of the desired character on sensitized paper by means of an electric current or beam of light. The paper then passes through a powdery black substance called toner, which contains dry ink particles. The ink particles are attracted to Nonimpact Printers Input and Output Devices 87 the exposed paper and the character becomes visible. These printers can print at speeds of from 3500 to 20,000 lines per minute. The laser printer form characters by projecting a laser beam of dot- matrix pattern on a drum surface. Toner is then attracted to the area exposed by the laser and transferred to the paper. The paper is then passed over a heating element which melts the toner to form a permanent character. Many types of ink jet printers are available. The simplest of these contains a series of ink jet nozzles in the form of a matrix. Vibrating crystals force ink droplets, roughly the diameter of a human hair, from selected nozzles to form an image in the same manner as an image is formed by a matrix printer. Different coloured inks may be used and combined to form additional colors. Several hundred nozzles are employed in the more sophisticated ink jet printers to direct a continuous stream of droplets across the page to form an image. These charged ink droplets travel at speeds of up to 40 miles per hour as they move between a set of plates that deflect the droplets. Droplets not needed are electrostatically attracted away from the paper for reuse. A stream of more than 100,000 droplets can form approximately 200 characters per second. 2.6 Plotters An inexpensive portable plotter capable of generating multicolor plots from data is stored on magnetic tape or disk. Plotters with multicolor capabilities generally use a writing mechanism containing several pens, each capable of producing a different color. Some devices for automated drafting are equipped with plotting surfaces larger than 10 square feet and cost as much as a minicomputer system. Whether an application is a general one (such as designing, mapping, or plotting schematics) or more specialized (such as three-dimensional data presentation, structural analysis, contouring, or business charts), there are plotters to do the tricks. 2.7 Microfilm Devices Computer output microfilm (COM) devices convert computer output to a human-readable form stored on rolls of microfilm or as microfilm frames stored on cards called microfilm. At speeds of 10,000 to over 30,000 lines per minute, COM is one of the fastest computer output techniques- more than ten times faster than the fastest impact printer. A single roll of Laser Printer Plotters Ink Jet Printers Computer Basics 90 Lesson 3: Other Peripheral Devices 3.1 Learning Objectives On completion of this lesson you will be able to : • know some special peripheral devices • understand characteristics and mechanism of such devices. 3.2 Terminals The terminal is a popular input/output device. Terminals are used for two-way communications with the CPU or with other terminals a few feet or thousands of miles away. With the aid of a terminal, a user can access computers around the world. Terminals, also called workstations, allow to interact with a computer. It is required to use a keyboard to enter data and receive output displayed on a cathode ray tube (CRT) display screen, or monitor. Because data must be keyed into these devices one character at a time, the possibility of error is high and the data transmission rate very low, thus, limiting the use of these terminals to small-volume input and inquiries. Terminal Functions Some of the functions that can be performed using terminals are the following: Message switching : The communication of information from one terminal to one or more remote terminals. Data collection: Data are input to one or more terminals and recorded on a secondary storage medium for subsequent processing. This eliminates the needs to record the information on a source document and then to key the information from the source document into the computer. Inquiry or transaction processing: Data stored in central data files can be accessed from remote terminals for updating or to determine answers to inquiries about information stored in these files. The system employed by most airlines to maintain and update flight information is an example of such a function. Remote job processing: Programs can be input from remote terminals directly to the CPU for processing. After execution, the results can be transmitted back to the terminal or to other terminals for output. Terminals are used for two- way communications with the CPU or with other terminals a few feet or thousands of miles away. Terminal Functions Input and Output Devices 91 Graphic display and design: Data can be displayed in graphic form, and can also be manipulated and modified. Interactive graphic displays, from simple home video games displayed on a television set to sophisticated computerized systems, provide complex designs and three- dimensional displays in either black and white or color. Terminals are available with features to suit the multitude of applications to which they are applied. In general three broad types of terminals are: point of sale, interactive remote, and intelligent. 3.3 Speech Recognition and Voice Response Devices Speech recognition devices were introduced in the early 1970s. Typically, these systems contain a database of stored voice patterns. This database of voice patterns is generally stored in a recognition unit or in secondary storage. A microphone, attached to the keyboard or recognition unit, records the spoken word patterns. A built-in microprocessor then compares, word by word, these patterns with the stored patterns and transmits the results of the comparisons to a computer for processing. A sentence must be spoken as a series of disjoined words and numbers spoken as a series of digits and not as a single number. Speech recognition devices are generally used in situations where access to a switch or control is not possible or where a user's hands are otherwise occupied. Because voice patterns vary greatly from person to person, most speech recognition services are speaker-dependent and must be fine-tuned to each operation. This is generally accomplished by having the operator speak each of the words or digits to be stored in the recognition unit dictionary several times. An average of the spoken voice patterns is taken and stored as the standard or mask against future voice communications will be compared. Speaker-independent systems are less common and have a very restricted vocabulary-generally the ten digits and a "yes' or "no" response. Despite their restricted vocabulary, speaker-independent systems are widely usable since they do not have to be fine-tuned but can be understood by anyone. Clearly, speaker-independent systems are more desirable than speaker-dependent systems. but their great expense, large database requirements and the limitations of current technology have made their development tiresomely slow. Speech recognition devices are currently employed in the preparation of numeric control tapes and in airline baggage sorting. Manufactures are beginning to offer very sophisticated speech recognition devices for the Speech recognition devices contain a database of stored voice patterns. Computer Basics 92 more popular microcomputers. For example, more than a dozen such devices are available for the IBM microcomputers alone. Voice response devices are commonplace in today's automated world. Warning sounds like "Warning! Warning! Your oil pressure is low" are being "spoken" by the voice response device in cars. The audio response is generally composed from a prerecorded vocabulary maintained in an external disk file. As an inquiry is received by the device it is sent to the computer for decoding. The computer then decodes and evaluates the inquiry and, from the prerecorded vocabulary on disk, constructs an appropriate digitally coded voice message, which is sent back to the audio response unit. The audio response unit then converts this message to a vocal reply, which is "spoken" to the inquirer. Such systems are not limited to one language. Vortrax, for example, manufactures an audio response unit that is capable of speaking in English French, German and Spanish. Computer generated voice output devices cannot reproduce the subtle shading of intonation commonly used in everyday speech. Their main advantage lies in the fact that they can be understood more than 99 percent of the time and that people respond more quickly to the spoken word than to the written word. Areas of application are generally characterized by situations that require responses to inquiries or verification of data entered directly into a computer system. Audio- response devices are used in banks for reporting bank account balance information, in large businesses for credit checking and inventory status reporting. and in experimental research to alert a worker who might otherwise be distracted or involved. One of the strongest impacts made on the use of voice response has come from the manufacturers of microcomputers. The pricing and availability of voice response units are economically feasible for even the smallest concern. Voice response is no longer an isolated, esoteric discipline but another among the multitude of computer output techniques. 3.4 Vision Systems A vision system utilizes a camera, digitizer, computer, and a technique known as image processing. Image processing is concerned with digitizing and storing of computer-processed images and with pattern recognition. Familiar examples of computer-processed images are: computer generated digitized portraits for a few dollars at most amusement parks, computer-produced special effects in movies such as Star Wars, Computer generated voice. A vision system utilizes a camera, digitizer, computer, and a technique known as image processing.