I-28 Computer Fundamentals
A CD is a shiny, silver colour metal disk of 12 cm in diameter. A typical optical disk is made
up of three layers: a polycarbonate base through which light can pass, a layer of aluminium
and a protective layer of acrylic on top of that. The pits of CD are typically 0.5 microns wide,
0.83–3 microns long and 0.15 microns deep. A CD has one track that spirals from the centre to
the outside edge. If one could remove the track from a standard 12 cm CD, it would stretch for
three and a half miles. The single track is divided into sectors of equal length and density. Files
are stored on these particular contiguous sectors. CDs are available in various formats, namely,
CD-ROM (compact disk-read only memory), CD-R (compact disk-recordable) and CD-RW
(compact disk-rewritable) disks.
(d) ‘DVD’ (‘Digital Versatile Disk’), initially called ‘Digital Video Disk’, is a high-capacity data
storage medium. At first glance, a DVD can easily be mistaken for a CD as both are plastic
disks 120 mm in diameter and 1.2 mm thick and both rely on lasers to read data. However, the
DVD’s seven-fold increase in data capacity over the CD has been largely achieved by tighten-
ing up the tolerances throughout the predecessor system. In DVD, the tracks are placed closer
together, thereby allowing more tracks per disk. The DVD’s track pitch (the distance between
each) is reduced to 0.74 micron, less than half of CD’s 1.6 micron. The pits, in which the data
is stored, are also a lot smaller, thus allowing more pits per track. The minimum pit length of a
single layer DVD is 0.4 micron as compared to 0.834 micron for a CD. With the number of pits
having a direct bearing on capacity levels, DVD’s reduced track pitch and pit size alone give
DVDs four times the storage capacity of CDs.
32. What do you mean by CD-ROM, CD-R and CD-RW?
Ans: A ‘CD-ROM’ disk comes with pre-recorded data by the manufactures and can be read but can-
not be altered. ‘CD-R’ is a type of ‘WORM’ (‘write once-read many’) disk that allows you to record
your own data. Once written, the data on the CD-R can be read but cannot be altered. A ‘CD-RW’ disk
is rewritable version of CD-R that means, it allows writing, erasing and rewriting of data several times.
The data recorded on all CD formats can be read using the CD-ROM drive; however, to write data on
CD-R and CD-RW disks, one needs a special peripheral device known as ‘CD-writer’ (or ‘CD-burner’).
33. Differentiate between magnetic storage and optical storage.
Ans: Though both magnetic and optical storage are the secondary memories, there is a huge difference
in their storage techniques, storage capacities, etc. Some differences between the two are listed in Table 1.5.
Table 1.5 Differences between Magnetic Storage and Optical Storage
Magnetic storage Optical storage
• Magnetic storage devices store the data in magnetic form.
• They tend to have large storage capacity as compared to opti-
cal media. For example, hard disks.
• They are optimized for high speed.
• Magnetic storage technology has been used for computers
since 1950. Thus, they are used to store important files and
software.
• They are affected by magnetic field.
• These storage devices are not as portable as optical devices as
they are mostly placed inside the computer. Moreover, if mag-
netic devices are kept near to a strong magnetic field area (such
as loudspeaker), then the device is more likely to get damaged.
• Optical storage devices store the data optically, that is, use
a laser beam to read/write.
• They have limited storage capacity as compared to magnetic
media.
• They are much slower as compared to the magnetic media.
For example, CDs and DVDs can access the data at a faster
rate to play music and movies, but are slower than hard disks.
• This technology is used for keeping portable data such as
movies and music.
• They are not affected by magnetic field.
• These storage devices are portable as they are smaller in
size, light weight and removable.
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Fundamentals of Computers I-29
34. A magnetic disk pack has 12 surfaces out of which 10 are readable. Each surface has 50
tracks and each track is divided into a number of sectors. If the total capacity of the disk
pack is 5,000 KB and the capacity of each sector is 512 bytes then:
(a) How many cylinders are present in the disk pack?
(b) How many sectors are present on each track?
Ans:
(a) Number of cylinders = 12 × 50
= 600
(b) Number of sectors =
×
=
5 000 1 024
512
10 000
, ,
,
35. What are input devices 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.
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 output device is just the opposite of the input device, that is, the data is 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 CPU, is in the form of digital signals.
The output devices display the processed information by converting them into graphical, alphanumeric
or audio-visual form.
36. List various input, output and input-output devices.
Ans: Some of the basic input, output and input-output devices are listed as follows:
• Input devices
Keyboard
Graphics tablet
Trackball
Barcode reader
Gamepad
Joystick
Microphone
Mouse (pointing device)
Scanner
Webcam
Touchpad
Light pen
Microphone
Electronic whiteboard
• Output devices
Monitor
Printer
Plotter
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I-30 Computer Fundamentals
Projector
Computer output microfilm (COM)
Speakers
• Input-output devices
Modems
Network cards
Touch screen
Headsets
Audio card/sound card
CD
Hard drive
Digital camera
37. Discuss the operations of the following devices:
(a) Light pen
(b) Touch screen
(c) Game controller
Ans:
(a) A ‘light pen’ (sometimes called a ‘mouse pen’) is a hand-held 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 that can be used directly on the monitor screen without requiring any special hand/eye
coordinating skills. As the light pen moves over the screen, the lines or images are drawn. The
working of light pen is as follows:
The light pen contains a lens and a photo detector located in its tip. When the electron beam
that sweeps the monitor strikes the phosphor within the light pen’s field of view, the light
emitted by the phosphor is focused through the lens and onto the photo detector. Due to this,
the signal current is increased and is transmitted to the computer. The position of the beam
is tracked by the horizontal and vertical counters, which relay this information to a register.
This cycle is repeated for every frame produced by the electron beam. By noting when a scan
goes by and measuring the interval between scan lines or entire screen refreshes, an accurate
position of the photo detector on the screen is determined. The light pen software generates
x-y vectors corresponding to a point on the screen, which may be used to make a selection by
activating a switch on the light pen.
(b) 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. Typically, it is used in information-providing systems
such as hospitals, airlines and railway reservation counters, amusement parks, etc. The working
of touch screen is described as follows:
A basic touch screen has three main components; namely, a touch sensor, a controller and
a software driver. 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
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Fundamentals of Computers I-31
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 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 touch-
ing 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 computer
to work together. It tells the operating system how to interpret the touch event information that
is sent from the controller.
(c)
A ‘game controller’ (also known as ‘joystick’) 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. Joystick also consists of
buttons which can be programmed to indicate certain actions once a position on the screen
has been selected using stick. It offers three types of control, namely, digital, glide and direct.
Digital control allows movement in a limited number of directions such as up, down, left and
right. Glide and direct control allow movements in all directions (360 degrees). 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 com-
puter games, training simulators, CAD/CAM systems and for controlling industrial robots. The
working of joystick is as follows:
A joystick is designed to inform the computer about the positioning of the stick at any
given time. This is done by providing the x-y coordinates of the stick. The x-axis represents
the side-to-side position and the y-axis represents the forward block position. The circuit
board that sits directly underneath the stick carries electricity from one contact point to
another. When the joystick is in neutral position, all but one of the individual circuits is bro-
ken. Each broken section is covered with a simple plastic button containing a tiny metal disc.
When the stick is moved in any direction, it pushes down on one of these buttons, pressing
the conductive metal disc against the circuit board. This closes the circuit, that is, it com-
pletes the connection between the two wire sections. When the circuit is closed, electricity
can flow down a wire from the computer and to another wire leading back to the computer.
When the computer picks up a charge on a particular wire, it knows that the joystick is in the
right position to complete that particular circuit. The joystick buttons work exactly the same
way. When a button is pressed down, it completes a circuit and the computer recognises a
command.
38. Explain in brief about OCR.
Ans: ‘OCR’ (‘optical character recognition’) is a software that scans the text document. This means
that OCR software translates the bitmap image of text to the ASCII codes that the computer can inter-
pret 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
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I-32 Computer Fundamentals
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.
39. Differentiate between hard copy and soft copy output.
Ans: The outputs, which can be easily understood and used by human beings, are of the two forms,
namely, hard copy and soft copy. These two are discussed as follows:
• Hard copy: The physical form of 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 micro-
film. 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.
• Soft copy: The electronic version of an output, which usually resides in computer memory and/
or on 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 soft copy form of output.
40. 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 132 columns of characters in each line, and prints either on single sheets, or on a continuous
roll of paper, depending upon the printer itself. The printers are divided into two categories which are
as follows:
Impact printers
An impact printer 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 which 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, whereas others can print an entire line. The three most commonly used im-
pact printers are dot matrix printers, daisy wheel printers and drum printers. Some characteristics of
impact printers are as follows:
• There is physical contact with the paper to produce an image.
• They are relatively cheap. The primary recurring costs for these printers are the ink ribbons and
paper.
• Due to being robust and low cost, they are useful for bulk printing.
• They can withstand dusty environment, vibrations and extreme temperature.
• They are ideal for printing multiple copies (that is, carbon copies) because they can easily print
through many layers of paper.
• Due to its striking activity, impact printers are very noisy.
• Since they are mechanical in nature, they tend to be slow.
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