computer Unit 4

Input and Output Devices
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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.

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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

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Figure 4.1 QWERTY Keyboard.
Figure 4.2: Dvorak Keyboard.
1.3 Other Input Devices
Punched Card
The punched card has served as an input medium to automated
computational devices. It has undergone little or no change since that
time, and most companies have phased out and replaced it with the more
efficient data entry media. Among the punched card devices still in use
is the punched card reader. The reading of punched cards takes place at
speeds ranging from hundred fifty to more than two thousand five
hundred cards per minute.
Punched card

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Key-to-Tape and Key-to-Disk Systems
In a key-to-tape system, data entered at a keyboard are recorded directly
on magnetic tape. The magnetic tape used is similar to the tape cartridge
or cassette used with home recorders. Accuracy is verified by placing the
recording tape into a magnetic tape verifier and having the original data
retyped. Magnetic tape encoders and verifiers are generally housed in
the same physical unit. Errors detected are corrected simply by erasing
the mistakes and substituting the correct character(s).
Character Readers
A character reader is capable of accepting printed or typed characters
from source documents and converting these data into a computer-
acceptable code. Currently available high-speed character readers are
capable of reading source documents at rates of up to several thousand
documents per minute and are costly. The three basic types of character
readers are magnetic-ink, optical mark, and optical character readers.
Magnetic-ink Character Readers
Magnetic-Ink Character Recognition (MICR) was developed by the
Stanford Research Institute for use by the world's largest bank, the Bank
of America. This system can read data prerecorded on checks and
deposit slips with a special ferrite-impregnated ink. The magnetized
characters can be read and interpreted by MICR equipment.
Character Readers
MICR

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-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).

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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

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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.

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Light Pen
The earliest pointing device is the light pen. This device is placed close
to a screen or monitor and turned on. A photo sensor inside the light pen
detects the scanning beam sweeping back and forth across the screen.
Accompanying circuitry converts the pen's reading into the position of
the pen on the screen. Light pens are used to select items from a list or
menu displayed on the screen. Light pens are used to select items from a
list or menu displayed on the screen and to draw graphic displays on the
video screen.
Digitizer Pad
A digitized pad looks like a graph pad with a pointer. It functions like a
light pen on a display screen except that the pad is mounted horizontally.
As the pointer is moved on the pad, the corresponding point on the
screen is illuminated. The digitized pad is useful in converting graphic
input, such as charts, graphs, and blueprints into patterns that can be
manipulated and stored by the computer.
Mouse
A mouse is a hand-movable device that controls the position of the
cursor on a screen. It has a box with buttons on the top and a ball on the
bottom. The box is placed on a flat surface, with the user's hand over it.
The ball's movement on the surface causes the cursor to move.
Joystick and Trackball
Joysticks are used with video games for user input. These devices may
also be used to move the cursor around a screen to facilitate input to a
graphical display. A trackball is similar in operation to the joystick. It
uses a billiard-sized ball to position the cursor. Several keyboard
manufacturers have integrated them directly into their keyboards.
Touchscreen
Touchscreen detects the touch of a human finger. One popular technique
used to detect the touch of a finger utilizes infrared light beams. In this
technique, infrared light beams shine horizontally and vertically on the
face of the screen. A pointing finger interrupts both horizontal and
vertical beams, pointing its exact location.
Light Pen
Digitizer Pad
Mouse
Joystick and Trackball
Touchscreen

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Pen drive
A pen drive is another name for a USB flash drive. Other names are
flash drive. USB flash drive, Thumb drive, etc. They are devices that
allow storage of computer files that you can remove and take from
computer to computer. The price of the driver is determined by the size
of its memory measured in megabytes or gigabytes. While 128 megabyte
drivers used to be considered large, current pen drivers sizes can reach
1,2,4 or more gigabytes. The drivers inserted in the computers USB
ports and are automatically recognized on PC operating systems beyond
Windows 98 (which needs a separate installation of drivers). Pen drives
can also have full blown application on them which are written in what
is called U3 compatible software.
Figure 4.6 : A Pen Drive.
Scanner
In computing an image scanner often abbreviated to just scanner is a
device that optically scans images, printed text, handwriting, or an
object, and converts it to a digital image. Common examples found in
offices are variations of the desktop (or flatbed) scanner where the
document is placed on a glass window for scanning. Hand-held scanners,
Where the device is moved by hand , have evolved from text scanning
“wands” to 3D scanners used for industrial design, reverse engineering,
test and measurement, orthotics, gaming and other applications
Mechanically driven scanner that move the document are typically used
for large-format documents, where a flatbed design would be
impractical.
Figure 4.7 : Scanner.

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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.

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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.

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Lesson 2: Output Devices
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.

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Monochrome or colour: Some monitors display images in only one
colour while others are capable of producing images in colours.
Monochrome monitors use a single electron beam and display one
colour, generally green, amber, or white, on a black background. The
phosphor composition of the screen determines the colour. Colour
monitors produce multi-colour images by combining the red, blue, and
green colours in varying intensities. Each pixel is made up of three
colour dots: red, blue, and green. It will appear to glow in different
colours depending on the intensity of each individual dot in the pixel.
Colour monitors are commonly referred to as RGB monitors since they
employ three election beams, one for each colour. Colour monitors are
categorized as CGA, EGA, VGA and SVGA depending on the
resolution. CGA monitors provide the least resolution (approximately
300 × 200 Pixels) and SVGA monitors provide the greatest resolution
(1000 × 800 pixels and greater).
Monitor interface: A monitor requires an appropriate interface to
communicate with a computer. For example, a colour graphics interface
board is needed for a colour monitor. This interface will generally not
work with a monochrome monitor and might even damage it. Dozens of
monitor interface boards are available for use with microcomputers. A
caution must be exercised to match the interface to both the monitor and
the computer.
Using a television: Some smaller microcomputer systems can be used
with a standard television. The basic difference between a monitor and a
television set is that the resolution of a television is substantially less
than that with a monitor. Also the television requires the use of a
modulator to interface the computer output with the television. The
modulator combines the separate audio and visual signals sent by the
microcomputer into a single modulated signal as required by a
television. Most inexpensive computer systems designed for use with a
television set generally have a built-in modulator.
Flat-Panel Displays
For laptop computers more compact, low-power, durable monitors are
used. A number of flat-panel display technologies are available for this.
The most common are the plasma and liquid crystal displays.
Plasma displays: A plasma display consists of an ionized neon or argon
gas (plasma) sealed between two glass plates. One plate encases a set of
fine horizontal wires and the other a set of vertical wires. Pixels are
formed by the intersections of the horizontal and vertical wires. A single
pixel can be turned on by sending a current through its horizontal and
vertical wires. This causes the gas between the wires to produce an
Monochrome monitors display
one colour. Colour monitors
produce multi-colour images by
combining the red, blue, and
green colour in varying
intensities.
A monitor requires an
appropriate interface to
communicate with a
computer.
Some smaller microcomputer
systems can be used with a
standard television.
Plasma displays.

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amber glow. The images produced by plasma displays are generally very
clear, and not subject to the flicker. Plasma displays are generally more
expensive than the CRT displays.
Liquid crystal displays: Liquid crystal displays (LCDs) have been used
for several years in calculators and digital watches. A thin layer of a
liquid crystal substance is suspended between two thin sheets of
polarized glass and separated by a wire grid into tiny squares. As current
is applied to the wires the liquid crystal substance within the square
changes from clear to opaque or black. The thousands of clear and black
squares produce patterns of characters.
The disadvantage of LCD displays is lack of brightness and resolution as
compared to CRT and plasma displays. The quality of the LCD display
depends on the surrounding light and the viewing angle. It is sharpest
and clearest when viewed in brightness from the front.
2.3 Printers
The printer is the most common output device. It produces permanent
visual record of the data output from a computer. It is capable of
producing business reports and documents currently available. Printers
are capable of printing from 150 to over 20,000 lines per minute, with
each line having up to 150 characters. Thus, a maximum printing speeds
of approximately 50,000 characters per second is possible.
Printers print on plain paper or on specially prepared single-or multiple
copy forms, such as invoices, stationery, labels, checks, bills and other
special-purpose forms used in business and industry. They can print both
text and graphics in black and white or in colour.
Printers can be subdivided into two broad categories, impact and non-
impact. The impact printers are the most common.
2.4 Impact Printers
In impact printers, printing occurs as a result of a hammer striking a
character form and the character form in turn striking an inked ribbon,
causing the ribbon to press an image of the character on paper.
Character printer devices print one character at a time at speeds of about
10 to 500 characters per second. The fastest of these printers is the wire
or dot-matrix printer. It prints characters made up of a pattern of dots
formed by the ends of small wires Figure 4.6 shows the letter "A" as
printed with different densities. By extending certain wires beyond the
Printer is the most common
output device. It produces
permanent visual record of
the data output from a
computer.
Liquid Crystal Displays
Impact Printers

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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

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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

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

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microfilm can store approximately 2000 frames and costs less than half
the cost to print the same amount of data on paper.
Because of the high cost of COM equipment, it is generally only
practical for larger businesses or industries generating approximately
several thousand documents per day. COM devices are commonly used
in libraries, mail-order concerns, defense installations, government
agencies, and similar, large operations.
Computer output microfilm
(COM) devices

89
2.8 Exercise
a. Multi-colour images are produced in combination of
(i) Red, green and blue
(ii) Yellow, red and blue
(iii) Black , blue and white
(iv) none of the above combinations.
b. Dot matrix printer is
(i) an impact printer
(ii) a non-impact printers
(iii) laser printer
(iv) none of these categories.
c. In general which one of the following is the best quality printer?
(i) Dot matrix
(ii) Ink-jet
(iii) Desk-jet
(iv) Laser.
a. What is pixel of a monitor?
b. What are the following acronym stands for : COM and LCD?
c. Describe flat-panel display.
d. What is the difference between ink-jet and laser printers?
e. What is the difference between printer and plotter?
3. Analytical questions
a. Describe monitor display of computer systems.
b. Describe details of different impact and non-impact printers.
c. Draw the diagram of an ink-jet printer process and explain it
briefly.

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Lesson 3: Other Peripheral Devices
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

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.

93
digitized images of Jupiter and Saturn beamed from image processors
onboard spacecraft to earth etc.
All of these examples have one thing in common that is to digitize an
image. In a visual system, all images that must be recognized or
interpreted must first be digitized and stored in a database. Only after the
database has been established the visual system can be applied to pattern
recognition. Pattern recognition, the process of interpreting images,
begins when the system digitizes the image of the object to be
interpreted. This digitized image is then compared to those in the
database to determine a probable match. As it is unlikely that a perfect
match will be achieved, there is always a small possibility of error.

Computer Basics
94
3.5 Exercise
(a) The terminal is
(i) input device
(ii) output device
(iii) input / output device
(iv) none of the above.
(b) Which one is the function of terminal?
(i) vision system
(ii) message switching
(iii) CRT
(iv) CPU.
(a) What is a terminal ?
(b) Briefly describe the functions of a terminal.
(c) What is the purpose of the vision system ?
(d) What do you understand of speech recognition ?
3. Analytical question
(a) Explain in details about the I/O devices that can be used as both
input and output devices.

computer Unit 4

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