BCA - FCIT - Sem I

Figure 6.17 : Scanner Input Devices
NOTES
These input figures, photographs, etc. in the computer memory in a digital state.
To scan a document using scanner it is placed on the levelled glass surface of the 101
scanner. Using the lense and light source, the picture is photosensed and turned into
a binary code and sent to the computer memory which shows it on the screen. We
can modify the scanned figure, if we want.
The greatest drawback of a normal scanner or image scanner is that it inputs the text
as images, which takes a lot of space on the harddisk. Optical character recognition,
optical mark reader, MICR scanners are its example.

OCR

Optical Character Recogniser is the technique in
which pre-printed charactersare distinguished by OCR
and recognised thereafter. OCR can read characters
printed by typewriter, character of cash register and
credit card. The OCR fonts are generally installed in
computer, they are also called OCR-standard.

OCR consists of special characters- letters, numbers Figure 6.18 : Optical Fonts
and special symbols - that can be read by a light
source that converts them into electrical signals that
can be sent to the computer for processing.
The most popular OCR input device is the
hand held wand reader as shown in Figure
6.18. The wand reflects light on the printed
characters, and the reflection is converted by
photoelectric cells to machine-readable code.
You often see sales people in departmental
stores use the wand to read retails tags and
send data to the store's computer for billing
and goods-ordering purposes.

OMR

Optical Mark Reader is a device which checks Figure 6.19 : A sample of Optical Mark
the presence and absence of the pencil mark Reader Sheet
on the paper. It reads the paper, by flashing
light on the paper and by receiving the
reflection of the paper. The concept behind
this technology is the absorption of light at
the pencil mark and hence there would be
less intensity of the light reflection from
that mark. We can only check a pre-defined
format paper by this technique.

Fundamentalsof This is most commonly used and suitable technique to check answer sheets in the
Computers & competitive examinations. In these competitive examinations in which the question
Information Technology paper is objective type and student has to mark one out of four or five options.

NOTES

Figure 6.20 : Optical Mark Reader

MICR

Magnetic Ink Character Recognition is widely used in banking where one has to deal
with a great number of cheques. MICR, known in short, is a method of machine-
reading characters made of ink containing magnetized particles. A special purpose
machine known as a reader/sorter reads characters made of ink containing magnetized
particles. E-13B and CMC-7 are two major fonts that are used globally.
In addition to their unique fonts, MICR characters are printed with a magnetic ink or
toner. Magnetic printing is used so that the characters can be reliably read into a
system, even when they have been overprinted with other marks such as cancellation
stamps. The characters are read with a device similar in nature to the head of an audio
tape recorder, and the letter for bulbous shapes ensure that each letter produces a
unique waveform for the read head.
This method is fast, accurate and automatic moreover the chances of errors are
negligible.
Required Devices For MICR
The necessary devices which use MICR are as follows -

 Special Magnetic Ink Printers or such laser printers which use MICR ink.
 MICR Fonts
 MICR Scanner
MICR Fonts
On special level, four types of fonts are used in check processing. These fonts are
called E-13B, CMC-7, OCR-A and OCR-B. OCR-A and OCR-B are generally used in
European countries.
E-13-B and CMC-7 are also called MICR Fonts, as they are to be printed with magnetic
ink which helps identify bank data. It is identified in the same way as your credit card is
identified. OCR-A and OCR-B are input through optical recognition.
E-13-B font was developed and adopted by ABA as a standard set. E-13-B is used in the
United States, Canada, Australia, Colombia Europe, Central America, India and other
eastern countries.

102 Figure 6.21 : MICR Fonts

CMC-7 font was developed by Machines Bull, a computer company of France. It has Input Devices
been in use in France since 1964, as a standard. In some countries of Europe and South NOTES
America too, this font is used. There are some countries where more than one types
of MICR Fonts are used in Bank Processing.
OCR-A and OCR-B are used in Austria, Belgium, portugal, Switzerland, Scotland and
several other countries.

Bar Code and Bar Code Reader

Bar code reader is one of the most popular input devices. It is used to read bar codes
written on the packet of the products. Bar code contains price and other product related
information.
A bar code has bars and blanks parallely attached. Predefined stripe and space patterns are
used to encode small sequences of character data in printed symbols. A bar code reader
is an input device that decodes the bar code. It is one of the popular and important input
devices. It reads the bar code and turns it into ASCII value which directly enters the
computers. A bar code reader scans the bar code through light source and measures the
reflected light. It creates two sorts of bars, black bars reflect less light while the white bars,
which are blank spaces, reflect more light.
Bar codes reader comes in two models -
 Flatbed model, that is used to provide information selected to the products in super

markets and big departmental stores.
 Handheld model, that is used to recognize products in the courier services.

Do ubl e-
check
Code

General Product Begin/End
category I.D. Code
Begin/End Code

Manufacturer I.D. Product I.D. number and
number and binary code binary code

Figure 6.22 : Bar Code

Figure 6.22 and Figure 6.23 depict the pictures of a Check Your Progress:
bar code and a bar code reader respectively. 4. What ar e t he t ypes of

Figure 6.23 :Bar Code Reader mouse?
5. What isscanner ?
AUDIO VISUAL INPUT DEVICES 6. What doyouunderstandby

Audio Visual input devices are such input devices, which input data or command M ICR ?
through sound or visual. The examples include Voice Recognition, Microphone, Digital
Camera etc. 103

Fundamentalsof Voice Recognition Devices
Computers &
Information Technology Voice Recognition is the latest advancement in the
computer technology. Using Voice Recognition device,
NOTES one can directly input data by dictating computer instead
of typing the data. This technology can also help to
overcome many shortcomings of traditional data input
system. Despite being very useful, this technology also
has drawbacks. This system recognises the voice of
speaker and words accordingly. Voice recognition device
has many other techniques for efficient data input.

Maximum Voice Recognition devices are speaker Figure 6.24 : Voice
dependent, hence these devices only understand the Recognition Hadset
word pronounced by single speaker (user). But there are
few Voice Recognition devices which are not speaker
dependent and do not have regular inputting facility.

Microphones

It is a common practice to input the instructions through sounds. In computers, Micro-
phone is used as a primary device to input sound. In this section, let’s see what Micro-
phone is.

The Microphone is an audio (sound) input device which is used to input the audio into
computer. Using the consignation of Microphone and speaker you can do voice-chat over
the internet. Apart prom this, it can also help you to record your voice. In order to use
it properly, it is necessary to have sound card in your computer.

Figure 6.25 : Microphone

Digital Camera

Digital camera is a mobile input device which can store any photograph or movie. We can
also view one stored picture or movie on the small screen attached with the camera.
Digital camera is a handy input device which can be taken from one place to another.

104

Figure 6.26 : Digital Camera

Automated Teller Machine Input Devices
NOTES
Automated Teller Machines or ATMs are won- Figure 6.27 : An ATM
derful devices we usually come across on the 105
bank campuses, shopping malls, railway stations,
airports, bus stands and other prominent market
and public places. These are actually special-
ized form of input devices for transaction pro-
cessing. ATMs allow you to withdraw money
even in the midnight (though some are for only
12 hours, most of them offer 24 hours service).
ATMs also allow you to make deposits, pay your
loans, pay bills and check your account transac-
tion and balance. You can use ATMs provided
you have an ATM card and a valid PIN (Personal
Identification Number). ATMs are connected to
the main computer of the bank and a very good
example of online processing system.

With the advent of ATMs, banking has become the easiest ever and people prefer doing
transactions with their ATMs as they feel relieved from queuing up in the bank's counters
for hours. On one hand, ATMs relieve the customers and save their time, while on the
other hand, have reduced cost of the banks on their human staffing and customers
satisfaction. Although ATMs have several advantages, a few disadvantages include power
failure and fraudulence of ATM cards.

SUMMARY

 Input devices are like our hand and feet through which we input our labor.

 A keyboard is a peripheral partially modelled after the typewriter keyboard.

 Keyboards are designed for the input of text and characters and also to control
the operation of a computer.

 Many companies have developed ergonomic keyboards which give more
comfort.

 Generally, the numeric keypad has 17 keys.

 Numeric keypad also has cursor movement keys besides the number keys.
These can be put on and off by Num Lock. When the Num Lock is On, only

number keys work and when Num Lock is Off the cursor movement keys will
work.

 Mouse is an online input device which is used to control the navigation of
pointer on screen.

 Major functions of a mouse include clicking, right clicking, double clicking and
dragging.

 There are three types of mouse namely Mechanical, Optical and Cordless.

 Optical mouse is a new type of non-mechanical mouse.

 Cordless mouse uses radio frequency to communicate information to your
computer.

 OMR is the most common technique to evaluate the answersheets of competitive
examinations.

Fundamentalsof  Optical Mark Reader is an input device which can recognise the pen or pencil
Computers & mark on paper.
Information Technology
 Optical Character Recognition is a technique which can recognise the character
NOTES by comparing it with OCR standard character.

106  Magnetic Ink Character Recognition is widely used technique in banking.
 In MICR technique, characters are printed on cheque by magnetic ink.
 MICR reader can read magnetic characters on cheque by magnetic coil

stimulation.
 Scanner is an input device.

 Scanner can input any picture or text written on paper directly into computer.
 OCR, OMR, MICR reader, are examples of scanner.
 ATM stands for Automatic Teller Machine.
 ATMs are specialized form of input devices for transaction processing.

Answer of the Check your progress :

1. We can classify the keys of keyboard in six types to understand its anatomy as-

 The Alphanumeric Keys
 The Numeric Keypad
 The Function Keys

 Special Purpose Keys.
 The Modifier Keys
 Cursor Movement Keys.
2. The Function keys–On the upper side of keyboard there are 12 Function keys
denoted by F1, F2,.....F12. These keys let you use commands in a short cut
manner. Functions of these keys change from software to software. However, F1
remains for Help in most of the softwares commonly used.
3. Positive Aspects :

 Free from wire
 Saving of desk space
 Key-board portability
Negative Aspects :

 Technical complexity
 Comparative costlier
 Less durable
4. Types of Mouse–There are three types of mouse -
 Mechanical Mouse

 Optical Mouse Input Devices
NOTES
 Cordless Mouse
Check Your Progress:
5. Scanner–Scanner is the input device which inputs data on the paper in the form 7. What isBar CodeReader ?
of graphics, picture or text, directly into the computer. The biggest advantage of 8. What do you known about
it is that one does not have to type the data.
digital camera?
OCR, OMR, MICR all are examples of scanner. 9. DefineOMR?

6. MICR–Magnetic Ink Character Recognition is widely used in banking where one 107
has to deal with a great number of cheques. MICR, known in short, is a method
of machine-reading characters made of ink containing magnetized particles. A

special purpose machine known as a reader/sorter reads characters made of ink
containing magnetized particles. E-13B and CMC-7 are two major fonts that are
used globally.

7. Bar Code and Bar Code Reader–Bar code reader is one of the most popular input
devices. It is used to read bar codes written on the packet of the products. Bar code
contains price and other product related information.

8. Digital Camera–Digital camera is a mobile input device which can store any photograph
or movie. We can also view one stored picture or movie on the small screen attached
with the camera. Digital camera is a handy input device which can be taken from one
place to another.

9. OMR is the most common technique to evaluate the answersheets of competitive
examinations. Optical Mark Reader is an input device which can recognise the pen
or pencil mark on paper.

EXERCISE

1. What are Input devices ? Classify them into different common categories.

2. Write down the names of any five input devices.

3. Explain the types of keyboards.

4. What are alphanumeric keys ?

5. Explain the design of a common keyboard.

6. What is a mouse ? Explain the chief functions of a mouse.

7. Write about different types of mice available in the market.

8. Write short notes on :

(a) OMR (b) OCR

(c) MICR (d) Joystick

(e) Touch Screen (f) Light Pen

(g) Digitizer Tablet (h) Track Ball

(i) Voice Recognition Devices (j) Bar Code Reader

9. Explain Ergonomic keyboard.

10. Write the positive and negative aspects of a keyboard with a chord.

11. What do you mean by scanner ? What does it do ?

12. Write about three different types of scanner.

Fundamentalsof 13. Differentiate between the functions of a Mouse and a Joystick.
Computers & 14. How many buttons are there is a standard Mouse.
Information Technology 15. What do you mean by dragging.
16. Write about three such devices in which a pen is used.
NOTES 17. Write the names of three such places where you have seen touch screen devices.
18. What do you mean by the resolution of a computer.
19. Name an Input Technique used in banking.
20. Differentiate between an OCR and scanner.
21. What is Bar Code. Tell about a Bar Code Reader.
22. What is the use of Automated Taylor Machine and which places are they found

at?

108

7 Output Devices Output Devices
NOTES
The Chapter Covers :
 Introduction
 Output Devices
 Soft Copy Vs Hard Copy Output
 Monitor
 Printers
 Plotter
 Electrostatic Technique
 Special Purpose Output Equipments
 Summary
 Exercise

INTRODUCTION

Output device is an important component of a computer.Whatever is said or done by your,
which is input by an input device and the way it has been executed by the central
processing unit is reflected on output devices. They are like our face where each and
everything reflects according to what goes on internally. There are a number of output
devices that help us see the result of our input. This chapter delivers information on
different output devices we use commonly as well as rarely.

109

Fundamentalsof OUTPUT DEVICES
Computers &
Information Technology An output device is a piece of hardware (a key physical part of a computer that can
be touched) which a machine, typically a computer, uses to present information to the
NOTES user. It can show any amount of information and any kind of information; for instance:
sound, data, memory, images etc. Common output devices include monitors, printers,
110 speakers, earphones and projectors.

SOFT COPY Vs HARD COPY OUTPUT

Generally we get result in two modes. These are called Soft and Hard. Generally, the
output we get is in two forms. Some of these can't be touched, while we can touch the
others and can keep them with us. For example the output we see on the screen, is only
visible, it is not in a tangible form. But the one we get through the printer, is tangible in
nature. The output which is not in tangible form is Soft output. Soft output is an output
which can't be recorded off-line. The visual display on the monitor, the sound of the
speaker etc. are the examples of the soft output. But the output that is in the tangible
form is called Hard Output. It can be recorded. The document printed out of the printer,
the maps printed by the plotter are the examples of hard output.

MONITOR

Monitor is an output device, where you can get your output on a TV-like screen. It
is commonly classified as - Monochrome, Gray-scale and Color, based on the colors
they display.
 Monochrome is derived from “Mono” which means single and "chrome" means

“color”; which means single colour. Monochrome monitors are single color monitor
like a black and white TV.
 Gray-scale monitors are special types of monochrome monitors for displaying
output in different grey shades.These monitors in flat-panel are commonly used in
handy computers.
 Color monitors can give output as a combination of RGB (Red-Green-Blue) radia-
tions. Due to RGB concept, they are capable of presenting graphics in a higher
resolution. If a computer has a sufficient memory, a color monitor can present
variety of colors ranging from 16 to 16,000,000 colors.

CRT Monitor

Most monitors are based on “picture tube element” like a television set. This tube is
known as “Cathode Ray Tube” or CRT in short. CRT technology is cheaper and capable
of presenting high quality colored outputs.

How CRT Monitors Work

CRT ( Cathode Ray Tube ) monitors consist of a vacuum tube with an electron gun.
In a monochrome monitor, a very thin electron beam is shot towards the plane surface.
The internal face of the plane surface has a phosphorus coating on it, which when fired
from electron beam emits lights which result in the formation of a single pixel. It may
be possible, that a continuous firing of electron beam, on a single point may burn
phosphorus at that point. To overcome this problem, the electron beam is shot in such
a manner that it travels in ‘Z’ path and activates the pixels on the screen to present
a visual output. The Z-type path of electron beam is called “Raster”.
The second side of picture tube which is called 'Neck' directs the path of electron beam
by regulating it through magnetic field.
When a pixel flashes for a while and extinguishes then a pixel is said to be refreshed. And
the rate at which refreshment of a pixel takes place is called Refresh rate which is
generally 30 times per second. When the refresh rate is low, screen flickers because

phosphorus loses its glow quickly. Output Devices
The luminescence of each pixel depends upon the intensity of electron beam which NOTES
further depends upon voltage of electric current. Voltage can easily be regulated. In a
digital monitor, presence and absence of voltage can put the pixels on and off, respec-
tively. In highly advanced analog monitors brightness of each pixel is controlled by a
continuous electron beam. In monochrome monitor this technology results in gray scale
effect; whereas in colored monitor CRT technology gives more variety of colors than digital
monitor.
The CRT of color monitor has some extra components. There are three electron guns for
red, blue and green colors. There is a triple phosphorous coating on the internal side so
that one pixel can emit three colours. Red, green, blue, and different tints and shades of
these colours can also be obtained by either increasing or decreasing the intensity of
electron beam.
All CRT monitors do not work on Raster Graphics. Some modern CRT monitors function
on Vector Graphic technology which is a high class technology and used to display anima-
tions and special graphics on the screen. (See Figure 7.1)

Figure 7.1 : Mechanism of CRT 111

Flat-Panel Monitors

Recently a new technology in the display devices has been developed. In this technology,
charged chemical gases adopt various chemical configuration to create images on the
screen. These are called Flat Panel Display. This device is light in weight and consumes
comparitively less electricity. This device is mainly used in laptop computers.
Flat panel monitors also have LCD technology which means Liquid Crystal Display. LCD
technology has less resolution than CRT technology hence clarity of output is also on the
lower side.
The two more technologies in Flat Panel Display are Gas Plasma Display or GPD and
Electro Luminescent Display or ELD. Both of these technologies viz, GPD & ELD have
better and high quality resolution but these are costlier too.

Liquid Crystal Display

A CRT monitor is just like your television. But today, with the evolution of technology, we
have started using LCD monitors. It's very attractive to look at. Let us discuss its advantages
and disadvantages and how it works.
Liquid Crystal Display is best known by its abbreviated form LCD. Is is digital display
technology which creates a figure on a flat surface with liquified crystals. It takes less space
and consumes less energy, and produces less heat than traditional Cathode Ray Tube
monitor. It has been in use for years as laptop screens. Now this screen is also in use for
desktop computers. It records several advantages on CRT monitor. This produce crisp text.
It is less than 10 inch thick. It has its demerits too. The colour produced by LCD can't

Fundamentalsof be compared to that of CRT monitors. They are almost 2 and ½ times costlier tham
Computers & CRT.
Information Technology The Liquid Crystal discovered in 1888 are liquified chemicals, the particles of which
can be aligned right within the electrical fields. It's as if the metal particles are aligned
NOTES when coming into the magnetic fild. When the particles are aligned properly light
moves through them.

Figure 7.2 : LCD Monitor

On laptop or desktop, the LCD screen multilayered is sanduciched keeping one end
high. A flurescent light source which is called backlight builds the first layer. Light first
passes through two polarizing filters. After that the polarizing light passes through a layer
in which numerous concentrated drops of liquid crystal are displayed in tiny cells. Then
those cells are displayed on the screen as rows. One pixel is a combination of one
or more cells. Pixel is the smallest point visible on display. The electric chords on a
side of the LCD create electric field, which folds the crystal particle and aligns the light
of another polarizing filter and lets it pass. At times, one on more pixels in the case
of electric current supply mechanism being failed, only black pixel is on display on the
monitor.
Almost in all the coloured LCD of the notebooks and desktops, a thin film transistor
which is called active matrix is used to activate every cell. TFT LCD create sharp and
bright images previous LCD techniques were slower and less efficient, and provided
lower contrast. Amids the oldest matrix technologies, a passive matrix present sharp
texts, but while changing fast display ghost images which is less suitable for motion
video. Today, in most of the black & white palm top and mobile phones, passive
matrix(C) are used.
Since LCD addresses each pixel separately, they the prepare texts faster than CRT,
which when focused beadly blurs all the clear pixels which creates the screen image.
But the high contrast of LCD can cause trouble when you want to display graphics.
CRT softens not only texts but also the edges of graphics and text, as a result it enables
one to read the text on lower resolution. It means CRT can apply better subtitutes in
the photograph than LCD does. LCD has one only natural resolution which limits the
pixels physically applied to the display. If you want to insert the resolution of 1024× 768
in an LCD of 800× 600 you have to immulate with the software which will work only
on an specific resolution.
Like CRT, the desktop LCD are made to accept the analog symbols from the PC which
are in wave form which is, infact in contrast of the binary wave form received from
the PC. It's so because till now most of the standard Graphics Boards convert the visual
information of their native digital form into analogbefore sendind it to the monitor. But
LCD process information in a digital form. Therefore, when the analog data from a
standard graphics board reaches to the LCD monitor, the monitor needs to convert it
again into digital form. Now digital LCD use the specific graphics board to sharpen the
display with digital connectors.
112 Advantages of LCD

 Requires less space

 Flickering is reduced. Output Devices
 Decreases energy consumption NOTES
 Reduces the expenses of electricity
Disadvantages of LCD 113
 Picture quality is comparatively not good.
 Picture could be viewed through only one angle.
 It is comparatively costlier than CRT.

CRT Vs LCD

Is this section, let is see what are the main differences between CRT & LCD. There
is a notable difference between CRT and LCD with respect to shape, size, cost and
working. Today the use of CRT is decreasing even with the desktop computers and
t is being replaced by LCD. Monitor the functionality of CRT & LCD monitor is also
different. LCD monitors have liquid crystals between thin polarized sheets. These liquid
crystals are in fact liquid charcoals. Because of this, the LCDs are thinner and one third
of that of CRT and it also emits less radiation. Hence, it also reduces the strum on
the eyes. But, LCD monitor also lass a drawback. It can be seen only at 160 degrees.
So, it is not clearly visible from the other side. The difference between these two is
explained in table 7.1 with the important points.

CRT LCD
1. It requires more space. 1. It requires less space.
2. Energy consumption is more. 2. Energy consumption is less.
3. The expenses on electricity are 3. It reduces the expenses forwards power

lighter. consumption.
4. It has good picture quality. 4. It does not have a comparatively better

5. In this, the result can be seen picture quality.
form different angles. 5. In this the result can be seen only from

6. It is cheaper. one dongle.
6. It is comparatively costlier them CRT

Table 7.1 : Major differences between CRT & LCD

Characteristics of A Monitor

A monitor incorporates the following characteristics :
Resolut i on

The most important factor of any display device is resolution; which can be
understood as the measurement of clarity of the visual screen or sharpness of
screen. In almost all display devices, images are formed because of various
electrified dots on the screen.
These tiny dots on the screen are called pixels. Pixel is the short form of “Picture
( say Pix) Element.” The number of pixels per unit area on a screen expresses the
resolution, quantitatively.
The more is the number of pixel on the screen, the more will be the resolution, i.e.
more sharpness and clarity of the graphics. For instance, if the resolution of a display
unit is 640 by 480, it means that this screen has 640 columns of dots and 480 rows
of dots on it.

Fundamentalsof Text character on the screen is composed of dot matrix. In general, size of the
Computers & matrix is 5× 7 = 35 pixels or 7× 12 = 84 pixels to display a text character on the
Information Technology screen. In this way, we can obtain about 25 lines with 65 characters each on the
aforementioned resolutions of the screen. We can also obtain higher resolution on
NOTES the screen.

Figure 7.3 : 640×480 pixel resolution Screen

Refresh Rate
Computer monitor continuously works, but the changes are so fast that it cannot
be experienced by our eyes. The image on computer screen keeps on changing
from left to right and top to bottom; as regulated through electron gun, but this
happens so fast that image seems stable on the screen. This can only be observed
when screen clicks. Refreshing of screen can only be observed in one condition
if its refresh rate is low. Refresh rate is measured in Hertz (Hz).

Dot Pitch
Dot pitch is a measuring technique to calculate the vertical difference between two
dots or pixels. Dot Pitch is measured in millimeter. This is a characteristic which
explains the quality of the monitor in terms of display. A color monitor used in a
personal computer has a dot pitch ranging from 0.15 to 0.30 mm. Dot pitch is also
called as Phosphor pitch.

Interlacing or Non-interlacing
Interlacing is a display technique which enables a monitor to enhance the quality
of its resolution. Electron gun in interlacing monitor can drow only half line as
interlacing monitor can refresh only half line at a time. These monitors can display
more than two lines at each refresh cycle.
On the other hand, the resolution given by non-interlacing is same as that of
interlacing, but latter is less expensive. The only drawback with interlacing type
monitor is that they have slow response time. The programs which require fast
refresh rate (Animation and Video) will flicker less. As resolution given by both of
these monitors is same but non-interlacing type is much better.

Bit Mapping
Initially, display devices were only character addressable which were capable of
displaying only text. The character displayed on the screen was equal in size and
composed of definite numbers of pixels. But due to continuously growing demands
of graphical display devices, the manufacturers of display devices were bound to
develop multipurpose display devices, which were capable of displaying both
graphics and texts.
The technique used to display graphical output is called Bit Mapping. Using this

114 technique, an operator can control each pixel on the screen and hence an operator
can draw any graphical image on the screen.

Video Standards or Display Modes Output Devices
NOTES
There are a variety of video standards that define the resolution and colors for displays.
They are explained here as follows– Check Your Progress:
1. What isan output devices?
(i) Colour Graphics Adapter (CGA) 2. What do you know about
(ii) Enhanced Graphics Adapter (EGA)
(iii) Video Graphics Array (VGA) soft copy and har d copy
(iv) Extended Graphics Array (XGA) output ?
(v) Super Video Graphics Array (SVGA) 3. Writ e t he advant ages of
Color Graphics Adapter (CGA) LCD.

It was first developed by IBM in 1981. This system was capable of displaying four 115
colors. Its displaying efficiency was 320 pixels horizontally and 200 pixels vertically.
This display system was first used for simple games incorporated with Windows, viz.
Solitaire and Checkers. But, this system was not suitable for Desktop Publishing and
other graphic images.
Enhanced Graphics Adapter (EGA)
This was also developed by IBM in 1984. This system was capable of displaying 16
colors. The displaying efficiency was better than EGA as it contained 640 pixels
horizontally and 350 pixels vertically. This system was more advanced than CGA and
could read text much easier. Despite this it wasn’t suitable for desktop publishing.
Video Graphics Array (VGA)
VGA Display system was developed by IBM in 1987. Now a days, many VGA monitors
are in use. The resolution of VGA monitor depends upon the color used in the system.
We can opt 16 colors with resolution of 640× 480 or 256 colors with 320× 200 pixels.
All IBM computers allow compatibility to VGA system.
Extended Graphics Array (XGA)
This display system was developed by IBM in year 1990. This system was the suc-
cessor of VGA, which was 4814/A display. The next version viz, XGA – 216, can give
one million colors with 800× 600 pixel resolution and 65536 million colors with
1024× 768 pixel resolution.
Super Video Graphics Array (SVGA)
Today almost all the PCs have SVGA graphics display system. Actually SVGA is different
from VGA but it is not a single standard in itself. In modern times, VESA ( Video
Electronic Standard Association ) has proposed a standard programming interface which
enables SVGA display system in PCs; it is called VESA BIOS extension. SVGA system
can display 16,000,000 colors. Smaller SVGA monitor can give resolution upto 800× 600
pixels and bigger SVGA monitor can give resolution of 1280× 1024 or 1600× 1200
pixels.

VESA
Video Electronics Standards Association, well known as VESA is an international
consortium founded by NEC Home Electronics and eight other video display adapter
manufacturing companies in the late 1980s. The goal behind formation of this
international standards organization was to standardize 800× 600 SVGA resolution
video displays. Since then VESA has issued several standards, mostly relating to
the function of video peripherals in IBM PC compatible computers.

Fundamentalsof PRINTERS
Computers &
Information Technology There are two limitations of display output devices -
(i) One can only see limited data at a time.
NOTES (ii) Output on screen is not transferrable and cannot be taken on paper.
Both the above mentioned limitations can be overcome by Printer as an output device,
which prints the output on the paper. The output on the paper in printed form is called
“Hard Copy”. The digital signals sent from computer are converted to natural languages
like Hindi, English etc. and then printed on paper by printer so that human being can
understand.
Printers can be classified on the basis of variety but on the basis of printing technology,
they are mainly categorized in two classes.

(a) Impact printers
(b) Non-impact printers
On the basis of the working speed they are categorized as
(a) Low speed printers which print one character at a time.
(b) High speed printers which print output as single line or whole page at a time.

Type of Printing Methods

On the basis of methods of printing, printers can be divided into Impact and Non-Impact.
Impact Printing
This printing type resembles with the printing by a typewriter. In this type of printer, a
metallic hammer or a print head strikes on paper and ribbon to print characters. In impact
printing, characters are printed either as dot matrix or as solid fonts on the paper. (See
Figure 7.4)
(a) Solid Font Method :

In this type of printing, a solid metallic typeset with characters embossed on them are
used.
(b) Dot matrix Method :
In this type of printing, a print head with vertical rows of pins is used. This printing
has higher speed than that of Solid Font printing. It generally has speed of 100 to 200
characters per second.

Figure 7.4 : Impact printing Figure 7.5 : Solid Font

116

Non-Impact Printing Output Devices
In this printing method, there is no direct striking between print head and paper. Non NOTES
-Impact printing can be of various types.
(a) Electro Thermal Printing : 117

In this printing method a print head with heated rod is used on a special type of
paper to obtain print. These are hard printers and requires a special paper to print
upon.
(b) Thermal Transfer Printing :
This is a new technology of printing in which the transfer of ink from wax-based
ribbon to the paper takes place.

MAJOR TYPES OF PRINTERS

Printer could mainly be classified into two categories input and Non-impact. Impact
printer prints with the printer, put pressure on the paper by making physical contact with
the ribbon. Non-impact printers display graphics and text without putting impact on the
paper. Printer can also be classified on the basis of their technique and printing method.
Ink-jet printer, laser printer, dot-matrix printer and thermal printer are some of then most
popular types of printer. In these, only Dot-matrix printer, is an impact printer, al the
others are non-impact printers.
Some of the printer, such photo printer, portable printer, multi-function printer and all-
in-one have been named on the basis of the specific tasks performed by them usually,
photo-printer and portable printer use the ink-jet print method, while multifunction printer
can use both the inkjet or laser technique.
Ink-jet and laser printer are widely used in homes and businesses. Dot-matrix printers
were in use during 60s & 70s, but, ink-jet printer have replaced them for home uses.
However, Dot matrix is still used in some types of businesses for multifaceted forms and
for cartoon copy. The use of thermal printers is limited to ATM, cash registers and point-
to-sale terminals. Some of the laser printers and portable printers also use thermal print-
ing.

Printer

Non-impact Impact
Laser printer
Dot-matrix printer
Ink-jet printer Daisy-wheel printer
Portable printer
Line printer
Photo printer Drum printer
Multifunction/all in
Chain printer
one printer

Thermal printer Band printer

Fig. 7.6 : Types of printers

Due to the popularity of Digital camera, lop-top and home office, the demand of
photo, portable and multifunction printers has tremendously increased in past few
years. Figure 7.6 illustrates different types of printers.

Fundamentalsof Inkjet Printer
Computers &
Information Technology Inkjet printers form characters on paper by spraying ink from tiny nozzles through an
electrical field that arranges the charged ink particles into characters at the rate of
NOTES approximately 250 characters per second. The ink which can be of various colors, is
absorbed into the paper and dries instantly. Printing on inkjet printers is expensive.

Figure 7.7 : Inkjet Printer

The main problem with these printers is ink clogging in the print head. The quality of
inkjet printer output is 300 dpi.

Now a days, most inkjet printers use thermal inkjet or phoelectric inkjet technology.
Thermal inkjet printer use heating substances. This heating object heats the ink and
creates vapour bubble which throws the inkdrops on paper through a nozzle. Most
inkjet manufactures use this technology in inkjet printers.

Pygoelectric inkjet technology is used in all the IPSON and Industrial Inkjet Printers.
In these printers, in place of the heating substance, in every nozzle pygoelecric crystals
are used, which change their form and shape, on the basis of the electric current, and
spray small inkdrops on paper. They use water ink which is a mixture of water, glycol
and colors. These inks are inexpensive but they can be used either on paper or on
a specially coated substances. In Pygoelectric inkjet printers one uses several types of
inke, solvent ink, dye-sublimation ink etc and it can print texts and graphics on many
encoated things. Inkjet head designs are divided into two main groups- fixed head and
disposable head. Fixed head is in-built and lasts till the printer lasts. It creates clearer
output than disposable heads. The ink cartridge of fixed head printers are inexpensive
for their print head can't be changed. But if the head goes out of order, the entire
printer is to be replaced. It increases the cost of ink-cartridge and the use of high
quality print head is restricted to them. But in them the print head disorder is not a
problem as it can be changed with new ink cartridges. Some printer manufactures use
disposable ink and disposable print head. They last longer than low cost disposable
head and are good for large amount of printing.

Advantages of Inkjet Printer :
 Low cost
 High level output. Clear printing.
 Deep-coloured printing
 Best for printing pictures
 Easy to use
 Quieter than Dot Matrix Printer
 No need of warm-up time

Disadvantage of Inkjet Printer :
 Print head less diviable. Print head clogging and more chances of their being
spoiled.
 Costlier to change the ink cartridge

118  Not good for big amount of Printing.

 Not fast like Laser Printer. Output Devices
 Paper looks clumsy due to ink leakage. NOTES
 Water sensitive ink out of which even one drop of water can mar the look.
 The use of highlight marker on Ink-jet printouts is difficult.
Many consumer inkjet printers are now a days available on less than Rs 1500. However
their prices have come down the price of their cartridge is getting higher. But the con-
sumer can re-fill it which reduces the printing cost 5-7 times.

Laser Printer

It is a non-impact printer. It is being used computer systems since 1970 in computer
system. First they were used in Mainframe computer. In 80's they were available for
microcomputer. These printers are more popular today, as they print text and graphics at
feader page and in high quality. When the speed and quality that is comparable to material
are required, a laser printer is the solution. Laser printer produces characters and other
images on paper by directing a laser beam at a mirror, which bounces the beam onto
drum. The laser leaves a negative charge on the drum, to which positively charged black
tones powder will stick. As paper rolls by the drum the toner is transferred to the paper.
A hot roller then bonds the toner to the paper.

Figure 7.8 : Laser Printer 119

Laser papers use buffers that store an entire page at a time. When a whole page is loaded,
it will be printed. Many laser printers designed to be used with micro computers can print
eight pages per minute. Laser printers designed for commercial use are much faster and
print approximately 20,000 lines per minute or 435 pages each containing 50 lines.

Most laser printers contain an additional microprocessor, RAM and ROM. ROM contains
the program that arranges Font and pages. It prints the best output. It prints in 300 to 600
dpi or great resolution. It has a special toner which contain particles of various colours.

Advantages of Lazer Printer :

 High Resolution (Normally 600 to 1200 dots per inch)
 High Printing speed.
 Blotless Printing.
 Per page printing cost is less than inkjet printer.
 Output is not water sensitive.
 Good for Printing in larger amounts.

Disadvantage of Lazer Printer :

 Costlier than the Inkjet Printer.
 Less capable in printing in various colors and high quality pictures, such as
photos.
 It is costlier to replace the toner and drum.
 Bigger and heavier tham the inkjet printers.
 Warm up time necessary.

Fundamentalsof Thermal Printer
Computers &
Information Technology Thermal Printers use two types of techniques
direct thermal and Thermal Transfer Printing. Tra-
NOTES ditional thermal printers use direct thermal
method. In this method, the pin heated by elec-
tricity is applied on heat sensitive or thermal Figure 7.9 : Direct
paper. On being heated, the paper coating gets Thermal Printer
black which forms the character and shape. Di-
rect Thermal printer does not use any ink or
toner a ribbon. These are durable and easy to
use and are less costlier in printing. But they are
affected by heat, light and greater, therefore the
text and images get deleted with time.

In Thermal Transfer printing, the thermal print head heats a heat sensitive ribbon which
makes the ink to melt on paper and creates text and shapes on paper. Its printouts are
every durable and can be saved for a long time.

Thermal printers are often used in cash registers, ATM and Point of sales terminal. Before
21st century, some old fax machines used direct thermal printing. Now they have been
replaced with laser and inkjet printers. It is still the best technique for bar code printing,
as it gives their accurate width and good quality image. Some Portable printers and most
table printers, even today, use thermal printing method.

Thermal Printer is not like inkjet. Inkjet print technology is applied in Thermal Inkjet Printer.
It heats the liquified ink and makes vapour bubble which helps the nozzle spray ink drops
on paper.

Photo Printer

These are colour printers which print the photo lab quality on paper. They are also used
for document printing. These printers have nozzles in large number which print good ink
drops for good quality image.

Some photo printers also have media card reader. They directly print the 4"× 6" photos
with the media card of a digital camera without any computers.

Figure 7.10 : Photo Printer

Most Inkjet Printers and high potential laser printers are capable of printing high quality
pictures. Sometimes these printers too are brought into the market as laser printers.
They are made to print photo on less cost and in good way. In addition to nozzles
in large numbers and very good drops, these printers have additional photo cyan, light
magenta and colour cartridges in light black colours. With these additional colours they
print more exciting and realistic photos giving better output than that of normal inkjet
120 and laser printers.

Multifunctional/All in One Printer Output Devices
NOTES
This printer is also called all in one printer or multifunctional device. It is a machine
which can work as several machines and printers, scanner, copier and fax. These are
very popular in home offices. They can use inkjet or laser print method. In some
multifunction printers, media card readers are used. They are inexpens sive to use and
occupy less space. But when any of the components breaks, you have to change the
entire machine.
Advantages of a multifunction printer

 Less cost : Buying a multifunction printer is economical than buying all the
devices (fax machine, scanner, printer, copier) separately .

 It requires less space
Disadvantages of a multifunction printer

 If a component breaks, the whole machine needs to be replaced.
 Entire machine is affected due to defects in any part.
 Print quality and speed is less than that of a individual printer.

Portable Printer

Portable Printers are small, light weight inkjet or thermal printers which allow one to
take a printout by Laptop computer during a journey. They are portable, easy to use
but more expensive than normal inkjet printers because of compact design. Their Print-
speed is relatively low. Some Printers are used to print photo then and there from the
digital cameras, that is why they are called portable photo printer.

Figure 7.11 : Portable Printer 121

Dot Matrix Printer (DMP)

It is an impact printer. In this printer, there is a print head which has a matrix of pins
in it. Each pin, when striked with ribbon, makes a dot on a paper.
Many dots constitute a character. Print head has vertical columns of 7, 9, 14, 18 or
24 pins. Pins of one column strike the ribbon to print dots at a time. In this way, a
single character gets completed in many steps. Print head forwards in the direction of
line.
Pins of print head receive the signals from CPU and mark the dots on the required
place on the paper.
Printing speed of Dot Matrix printer is about 30 to 600 characters per second. Many
dot matrix printers can print lines from left to right as well as from right to left. When
print head completes the line by moving left to right, then it starts writing the next
line from right to left.

Fundamentalsof
Computers &
Information Technology

NOTES

Figure 7.12 : Dot matrix Figure 7.13 : Dot matrix print head
printed C character

A dot matrix printer can print graphics of any shape and size and character of any
language. Characters are made with the help of print head which receives signals in
binary code. An electronic circuit decodes the characters. Clarity of characters in dot
matrix is generally less than that of solid font printers.

This printer can print in following two qualities:

(i ) Draft Quality Printing – It is general printing with low quality.

(ii) Near Letter Quality Printing– It is a bit higher quality in which each character
is printed by double overstrike. This printing is slower than the former one.

Advantages of Dot Matrix Printer :

 Capable of printing on a multifaceted form or carbon copies.
 Per page printing cost is less.
 Useful for printing and data logging on continuous form paper.
 Reliable and durable

Disadvantage of Inkjet Printer :

 Creates loud noises.
 Limited Printing quality.
 Low Printing Speed.
 Printing with a few colours.

Daisy Wheel Printer

Daisy wheel printers are solid font type character printers and give good quality prints,
similar to typewriters. Daisy wheel printer is so called because the print mechanism looks
like a daisy; at the end of each “petal” is a fully formed character that produces solid line
print. A hammer strikes a petal against the ribbon, and the characters print on a paper.

122 Figure 7.14 : Solid font on
Daisy wheel spokes
Figure 7.15 : Daisy Wheel Printer

The daisy wheel can be replaced to change styles and sizes of typefaces (fonts). For Output Devices
example, the daisy wheel can shift from character to symbols, or they can print text NOTES
in foreign language. Daisy wheel printers usually operate at 90 characters per minute.

Line Printer

For certain operations in business where an enor-
mous amount of printing needs to be done, charac-
ter-at-a-time printers are just too slow. Line Printers
or line-at-a time printers, use special mechanisms
that can print a whole line at once, such printers can
typically print from 300 to 3000 lines per minute.

Different types of line printers are –

  Drum Printer Figure 7.16 Line Printer
  Chain Printer
  Band Printer

Drum Printer

Drum Printer has complete character sets engraved around the circumference of the
drum at each of the print positions. The number of print positions across the drum equals
the number available on the page, typically ranging from 80 to 132. Individual print
position rotates until the desired letter is in the proper place; then the hammer strikes the
paper against the ribbon and the drum, producing the entire line of print. (See Figure 7.17)

Band

Figure 7.17 : Drum used in Drum printer

Chain Printer
Chain Printer uses a chain of print characters wrapped around two pulleys. Like the drum
printer, there is one hammer for each print position. Circuit inside the printer detects when
the correct character appears at the desired print location on the page. The hammer then
strikes the page, pressing the page against a ribbon and the character located at the desired
print position. An impression of the character is left on the page. The chains keep rotating
until all of the required print positions on the line have been filled. Then the page moves
up, to print the next line. (See Figure 7.18)

123

Figure 7.18 : Chain printer

Fundamentalsof Band Printer
Computers & Band Printer operates in a similar way except that it uses a band instead of chain and
Information Technology has fewer hammers. The hammers on the band printer are mounted on a carriage that
moves across the paper to the appropriate print positions. Characters are rotated into place
NOTES and struck by the hammers. Font styles can be changed easily by replacing a band or chain.
(See Figure 7.19)

Figure 7.19 : Band printer

PLOTTER

The growth of computer aided design and drafting has created a demand for device that
can produce high quality graphics in multiple colors. A plotter reproduces drawing using
pens that are attached to movable arms and are directed across the surface of a stationary
piece of paper. Many plotters, however, combine a movable pen armed with paper that
can also roll back and forth to make the drawing. This two-way movement allows any
configuration to be drawn.
Plotter applications are not limited to computer aided design. High quality bar graphs and
pie charts created with plotter can add interest and meaning to business presentations.
One can print charts, drawings, maps and three dimensional illustrations with plotter.
Generally, plotter are of two types

  Drum pen plotter
  Flat bed plotter.

Figure 7.20 : Plotter

Drum Pen Plotter

This is an output device which uses a pen type structure, which moves on paper surface
to draw a graphic. A paper rolls along by the drum and this pen draws graphical illustrations
like a mechanical artist under the control of computer. The colour presentation by plotter
is excellent. Plotters also have fibre-tipped pen, but when high quality is desired then
technical drafting pen is used. This pen is capable of drawing a line even equal to the
124 thousandth part of an inch. Colored plotters may have four or more than four pens. A
plotter plots a drawing with a steady rate of few inches per second.

Flat Bed Plotter Output Devices
In this type of plotter, paper is kept on a stable non-moving bed or tray. An arm with a NOTES
pen driven by motor is incorporated throgh, this arm the plotter draws graphics, under the
control of instructions given by computer, along X-axis and Y-axis. (See Figure 7.20) 125

ELECTROSTATIC TECHNIQUE

In this technique, the pen is replaced by a toner bed. It works like a Xerox or Photostat
machine but has a different mechanism. Unlike Photostat machine, a network matrix of
five wires is used to charge the paper, instead of any optical resource. When the charged
paper is passed through toner, then toner gets stuck to paper resulting in the formation
of image, picture, graphics etc.
A flat bed electrostatic plotter is high speed plotter, but it lacks in quality when compared
with Pen Plotter.
Pen technique and electrostatic technique both can be used in drum plotter and flat bed
plotter as well.

SPECIAL PURPOSE OUTPUT EQUIPMENTS

This segment of the chapter throws light on some output devices which are being used
for special purposes. These are –

• Computer Output Microfilm
• Film Recorder
• Voice Output Devices

Computer Output Micro-film (COM)

This is the technique of producing the computer output through microfilm media. Micro-
film media can be a microfilm reel or micro film card. This technique helps in saving the
cost of papers and problem of storage space.
For example, a microfilm card of size 4× 6 inch can store the data equivalent to 270
printed papers of normal size. COM technique is used in such offices where data and
information are generally not modified or amended and number of data files is big. The
preparation of microfilm is an offline process. First of all computer stores the data on a
magnetic tape storage medium. Then using a COM unit, each page of data is first
projected on screen and then its photographs are made on microfilm. COM unit can also
work online with computer.
To read the output from microfilm, mini computers have a special device which can display
the output in frames.

Film Recorders

A film recorder is a camera type device which
can transfer computer generated high resolution
graphics directly to 35 mm slide, film or on
transparencies. Previously this technique was
used with big computers but today it is avail-
able even with micro computers.
Several companies prepare presentations to
propagate their products. These presentations
are made by using film recording techniques
only. (See Figure 7.21)

Figure 7.21 : Film recorder

Fundamentalsof Voice Output Device
Computers &
Information Technology When we dial a number to our friend, sometimes we receive a message by an
answering machine intimating his absence and asking for leaving message. These types
NOTES of pre-recorded messages are played by voice output devices. In these devices,
computers store different words in a file to constitute a message. These types of devices
126 have a huge vocabulary of pronunciations and will constitute messages as per instruction
by computer programs. The voices are then delivered to user by speaker.

Sound Card and Speaker

A sound output in computer is used to receive message in games and other programs.
A sound card is a device which provides a computer with good quality and better output
in voice. It is an attachable type device and can be inserted into the free slot of the
mother board. The general purpose for which sound card is used is the use of multimedia.
Before attaching a sound card, we must check the sound card’s compatibility with com-
puter system. Before installing sound card we must also confirm that it should not induce
any conflict with pre-installed external device in the computer. The sound card installation
requires few default settings so that it can become customizable with a computer system.
A speaker is a device which can give actual voice output in the form of voice and music.
Speaker is also an output device which presents output of any program sound. By using
speaker we can listen to sounds of music, movies and game tunes.

Earphones

Headphones (also known as earphones, earbuds, stereophones, headsets, or by the slang
term cans) are a pair of transducers that receive an electrical signal from a media player
or receiver and use speakers placed in close proximity to the ears (hence the name
earphone) to convert the signal into audible sound waves. In the context of telecommu-
nication, the term headset is also commonly understood to refer to a combination of
headphones and microphone used for two-way communication, for example with a mobile
phone.

Projectors

Projectors are used for displaying an image on a projection screen or similar surface for
the view of an audience. There are a variety of projectors as follows :
Video projector
A video projector takes a video signal and projects the corresponding image on a projection
screen using a lens system. All video projectors use a very bright light to project the image,
and most modern ones can correct any curves, blurs, and other inconsistencies through
manual settings. Video projectors are widely used for conference room presentations,
classroom training, and home theatre applications.
A video projector may also be built into a cabinet with a rear-projection screen to form
a single unified display device, now popular as “home theater” applications.
Common display resolutions for a portable projector include SVGA (800× 600 pixels), XGA
(1024× 768 pixels), and 720p (1280× 720 pixels).
Movie projector
A movie projector is an opto-mechanical device for displaying moving pictures by
projecting them on a projection screen. Most of the optical and mechanical elements,
except for the illumination and sound devices, are present in movie cameras.
Slide projector
A slide projector is an opto-mechanical device to view photographic slides. It has four
main elements: a fan-cooled electric light bulb or other light source, a reflector a

holder for the slide and a focusing lens. A flat piece of heat absorbing glass is often Output Devices
placed in the light path between the condensing lens and the slide, to avoid damaging NOTES
the latter. This glass transmits visible wavelengths but absorbs infrared. Light passes
through the transparent slide and lens, and the resulting image is enlarged and
projected onto a perpendicular flat screen so the audience can view its reflection.
Alternatively, the image may be projected onto a translucent “rear projection” screen,
often used for continuous automatic display for close viewing. This form of projection
also avoids the audience’s interrupting the light stream or bumping into the projector.

Figure 7.22 : Slide Projector

Slide projectors were common in the 1950s and 1960s as a form of entertainment. Check Your Progress:
4. DefineResolution.
SUMMARY 5. What aredisadvantages of

 Input and output devices serve for the communication between computer and Inkjet Printer ?
human being. 6. What isDrumPrinter ?
7. What isProjector ?
 Computer presents result after the processing through the output device.
127
 The screen is a display device which is technically called a Visual Display Unit.

 When output is in the form of alphabet, numbers and symbols, it is called text
output.

 When output is given in the form of photograph and diagrams it is called
graphical output.

 Resolution is the clarity of the display devices.

 Pixel is the smallest dot on the screen which emits light radiations to form
images on the screen.

 Screen of a computer is Cathode Ray Tube.

 Laptops have Flat Panel Display.

 Flat Panel Displays have Liquid Crystal Display technique.

 CRT works on the Raster principle.

Fundamentalsof  Printer is an online output device which prints output on a paper or a sheet.
Computers &
Information Technology  Output can be printed on paper by impact and non-impact printing methods.

NOTES  Impact line printer can be of three types namely Drum, Chain and Band
Printers.
128
 Computer Output Microfilm is a technique to print output on a microfilm
media.

 Voice Output Devices present output in the form of sounds.

 Dot pitch is a measurement technique which measures a difference between
pixel.

 Sound output is used to receive message in games and music tunes.

 Projectors are used for displaying an image on a projection screen or similar
surface for the view of an audience.

Answer of the Check your progress :

1. Output Devices–An output device is a piece of hardware (a key physical part
of a computer that can be touched) which a machine, typically a computer,
uses to present information to the user. It can show any amount of information
and any kind of information; for instance: sound, data, memory, images etc.
Common output devices include monitors, printers, speakers, earphones and
projectors.

2. The output we see on the screen, is only visible, it is not in a tangible form. but
the one we get through the printer, is tangible in nature. The output which is
not in tangible form isSoft output. Soft output isan output which can't be recorded
off-line. The visual display on the monitor, the sound of the speaker etc. are the
examples of the soft output. But the output that is in the tangible form is called
Hard Output. It can be recorded. The document printed out of the printer, the
maps printed by the plotter are the examples of hard output.

3. Advantages of LCD :

Requires less space

Flickering is reduced.

Decreases energy consumption

Reduces the expenses of electricity.

4. Resolution–In almost all display devices, images are formed because of vari-
ous electrified dots on the screen. These tiny dots on the screen are called
pixels. Pixel is the short form of “Picture ( say Pix) Element.” The number of
pixels per unit area on a screen expressesthe resolution, quantitatively.

5. Disadvantage of Inkjet Printer :

• Print head lessdiviable. Print head clogging and more chancesof their being
spoiled.

• Costlier to change the ink cartridge

• Not good for big amount of Printing. Output Devices
NOTES
• Not fast like Laser Printer.
129
• Paper looks clumsy due to ink leakage.

• Water sensitive ink out of which even one drop of water can mar the look.

• The use of highlight marker on Ink-jet printouts is difficult.

6. Drum Printer–Drum Printer has complete character sets engraved around the
circumference of the drum at each of the print positions. The number of print
positions across the drum equals the number available on the page, typically
ranging from 80 to 132. Individual print position rotatesuntil the desired letter
is in the proper place; then the hammer strikes the paper against the ribbon
and the drum, producing the entire line of print.

7. Projectors–Projectors are used for displaying an image on a projection screen
or similar surface for the view of an audience.

EXERCISE

1. What is a pixel ?

2. What do you understand by CRT ?

3. Name the technologies in Display Devices.

4. What do you understand by refreshing a screen ? What is the refreshing rate of
a screen in general?

5. What are line printers ? State two examples.

6. What are drum printers?

7. Explain any three printers in detail.

8. What is a monitor ? Write characteristics of a monitor in detail.

9. What is a plotter ? Explain various types of plotter in detail.

10. Write an elaborate note on projectors.

11. Write five advantages and disadvantages of LCD.

12. Give five differences between LCD and CRT monitor.

13. What is soft copy ?

14. What do you mean by Hard copy ?

15. Explain LCD monitor in detail.

16. What do you mean by Resolution ?

17. What is Refresh Rate ?

18. What is Dot Pitch ?

19. Tell about VESA.

20. Write a short essay on the printers available in the market.

Fundamentalsof 21. Explain the functions of an imkjet Printer.
Computers & 22. Write the advantages and disadvantages of on inkjet printer.
Information Technology 23. Write the advantages and disadvantages of a Laser Printer.
24. Write the advantages and disadvantages of Dot Matrix Printer.
NOTES 25. Differentiate between Laser and Inkjet Printers.
26. What is an earphone? Explain.
27. What do you mean by computer output microfilms ?
28. What is a Film Recorder.
29. Write a note on Sound Card and Speaker.

130

8 Central Processing Unit Central Processing Unit
NOTES
The Chapter Covers :

 Introduction
 What is Central Processing Unit
 Arithmetic And Logic Unit
 Control Unit
 Registers
 Instruction set
 Processor Speed
 Summary
 Exercise

INTRODUCTION

Computer anatomy basically depends upon the part of a computer called central processing
unit, where input data are processed and turned into information. This chapter presents
an elaborate discussion on various parts of central processing unit.

131

Fundamentalsof WHAT IS CENTRAL PROCESSING UNIT ?
Computers &
Information Technology C.P.U., an acronym for Central Processing Unit, is supposed to be the brain of
computer. It mainly executes the programs and controls different parts of a computer
NOTES such as memory, input and output devices. Programs and data are stored under its
control. It helps you see your output on the screen and get print out on the paper
through printer.
Central processing unit includes mainly 3 parts. They are as follows :

 Arithmetic & Logic Unit
 Main Memory Unit
 Control Unit

ARITHMETIC AND LOGIC UNIT

Arithmetic and Logic Unit is known as A.L.U. in short. This unit performs mathematical
operations as well as logical operations on data. It contains an electronic circuit, that can
do calculations like addition, subtraction, multiplication and division of binary arithmetic.
A.L.U. primarily convertsin simple arithmetic operations like multiplication becomes multiple
times addition and later gets transmitted after converting them into electrical pulses.
In logical operations, A.L.U. compares two numbers and data and makes decision while
processing.
A.L.U. takes instructions or guidelines from Control unit. It gets data from memory and
returns information to the same. A.L.U. works amazingly fast. Its estimated speed is about
1000000 calculations per second. It contains several registers and accumulators which work
as virtual memory during calculations. A.L.U., as instructed by control unit according to the
programs receives data from memory and places them on accumulator.
For example, you are to add two numbers A and B. Control unit selects A from memory
and adds to B available in A.L.U. output gets placed in memory or for future calculation,
it is stored in accumulator.

Memory

C.U

132 Accumulator
Register
A.L.U.

Fig. 8.1 : Calculation in ALU

Arithmetic Operations Logical Operations Central Processing Unit
+ Addition NOTES
– Subtraction =, = equal, unequal
* (× ) Multiplication >, > greater, not greater Check Your Progress:
greater or equal, greater or not equal 1. What doyouunderstandby
¸ (/) Division ,
CPU ?
, less or equal, less or not equal 2. What are mai n par t s of

Table 8.1 : Operations in A.L.U. CPU ?
3. DefineControl Unit ?
CONTROL UNIT
133
Control unit controls the internal process of a computer. It controls the input and output
processes of the computer. It also directs the exchange of data and instructions
between memory and ALU.
It receives the instructions of a program to execute the program itself from memory.
Then it converts the instructions into electronic signals and delivers them to the
appropriate devices to complete the data processing. Control unit also directs the ALU
about the location of the data to be processed in the memory. The control unit also
instructs the ALU about what operations to be performed, and after processing, where
to store the output. The instructions in the form of signals are sent to various parts of
computers through the control bus of a system bus. A combination or group of wires
is called a bus. This bus carries electronic signals through out the system unit. They
are named on the basis of the type of signals they carry. The main bus of a system
unit is called System Bus. And the bus used for the transportation of control signals
is called control bus.

REGISTERS

Computer instructions are carried out by the C.P.U. To execute instructions, information
is exchanged. C.P.U. of computers uses a memory unit to exchange information fast
and satisfactorily. This memory unit is called a register.

Registers are not the part of main memory. They store information for time being. Size
of a register equals to the capacity of its storage of bit. For instance, if a register can
store 8-bit then it is called as 8-bit register. Nowadays, 16-bit registers are in vogue
while 32-bit and 64-bit processors are also in use. The more bit, registers would have,
the faster data processing of computer will be. Computer has got following types of
registers :

 Memory Address Register

This stores active memory location of computer instructions.

 Memory Buffer Register

This register stores the contents read from or written onto memory.

 Program Control Register

This stores address of the instructions to be executed next.

 Accumulator Register

This register stores the middle and last result of the data being
executed. Normally, these registers are used while execution of
information.

 Instruction Register

These registers store instructions to be executed.

 Input/Output Register

These registers are used to communicate information between input
and output devices.

Fundamentalsof BUS
Computers &
Information Technology Let us discuss what a bus is. It acts like a path between the components of computer.
A computer has two main buses. First Internal or system bus and second, external or
NOTES expansion bus. The system bus is situated on the motherboard and links the CPU with
other devices on the motherboard. The task of expansion bus is to link CPU with external
134 devices for example- key-board, mouse, modem, printer etc. The chords of disk drive and
other devices are plugged in the bus. The system bus has two parts- data bus and address
bus. Data bus is an electrical path which attaches, CPU, memory and other hardware
devices. In fact, a bus is a set of parallel chords. The number of chords in the bus affects
the transaction of data between hardware components. Because, every chord can transfer
1 bit of data at a time. One eight chord bus can carry eight bits, it means one byte at
a time. Address bus too is a set of chords like data bus. An address bus links only a CPU
and RAM and carries memory address only. Every byte in the RAM is attached to a number
which is its memory address.

INSTRUCTIONS SET

Let us see what an instruction set is. Every processor accomplishes tasks like receiving
character from the memory or getting a large numbers after comparing between two
numbers. All of these operations have their own number which are called instructions. The
list of instructions in a processor is called instruction set. Each processor has its our
instruction set. That's why a program is developed after keeping a specific processor in
mind.
C.P.U. instructions, which are for executing commands, are prepared in a control unit.
Instructions or Instructions sets list such operations that C.P.U. can perform. Each instruction
of instructions set is represented in micro codes that instructs C.P.U. about how to carry
out complex operations.

PROCESSOR SPEED

Processor speed stands for the speed at which the CPU executes the instructions. It is
measured in megahertz (MHz).
Processor speed depends upon data bus being used by the processor. Data bus is used
to trensfer data on the processor. These data buses come in 8-bits, 16-bits, 32-bits, 64-
bits and 128-bits. 8-bits means, it can transfer 8 bits (1 byte) data at a time. Likewise, 128
bits data bus can transfer 128 bits of data at one time. The bigger the size of data bus
is, the speedier the processor will be.

SYSTEM CLOCK

Let us see what role a system clock plays in a computer. The events inside a computer
take place at a decided speed which is controlled by an electronic drummer. It is called
system clock. This part is an electronic circuit which create pulses at a fast speed which
is measured in millions of cycles per second. The rate of the processor clock is called its
clock speed, and one pulse is called clock tick. The system clock normally does nothing
to maintain time and date. To do all these things there is a separate circuit in all the
computers. The system clock synchronizes the internal activities of a computer.

CISC and RISC

CISC stands for complex instruction set computer. CISC chip, for ex. Motorola 68040 or
Intel, provide several instructions to pentium programmers. In addition, it has a processing
circuitary which has many specific purpose circuits which implement these instructions at
a high speed, For in chips, there are so many processing tools. CISC design makes the
work of a programmer easier. CISC chips are complex and costly and get heated because

of consuming a log of electricity. RISC refers to Reduced Intruction set computer. A Central Processing Unit
RISC chip provides bare bonus instruction set. It's why RISC chip are less expensive NOTES
and more power efficient. The demerit of RISC design is that the computer has to
repeat the operations to complete many processing activities. CISC chips provide faster
processing than that of SISC chips.

POPULAR MICROPROCESSORS

You read about processors in chapter 2. We had discussed about Intel processors in
detail. Intel is, of course, the first processor manufacturing company and the most
popular even today. But now, there is not only Intel in the market. Let us know about
the ones available in the market. They are generally three - Intel, AMD and IBM.
Intel Processor

Intel corporation is largest Micro Processor manufacturing company. The
processors developed by it are called Intel. They are mostly used in Micro :
Personal computer. Celeron, Pentium, Itanium etc are its famous family.
AMD Processor
Its complete form is Advanced Micro devices. It is the second most popular
processor after Intel. It main family members contain- Duron, Athelon, Optron
etc.
Motorola Processor
Motorola Processor is the processor made by Motorola company. These are
known as Freescale Processor. Almost all Apple computers use this very processor.

SUMMARY Check Your Progress:
4. What isRegister ?
 Computer anatomy basically depends upon the part of a computer called 5. What isAccumlator Regis-
Central Processing Unit.
ter ?
 Central Processing Unit is supposed to be the brain of a computer. 6. What does RISCand CISC
 Central Processing Unit executes the programs and controls different parts of
st and for-
a computer such as memory, input and output devices.
 Arithmetic and Logic Unit is known as ALU in short. 135
 ALU performs mathematical operations as well as logical operations.
 Control Unit controls the internal process of a computer.
 In order to execute instructions information is exchanged. CPU uses a

memory unit to carry out this exchange of information speedily and satisfactorily.
This memory unit is called a register.
 Registers are not the part of main memory. They store information temporarily.
 Processor speed is measured in MegaHertz (MHz).
 The system clock synchronizes the internal activities of a computer.
 CISC stands for Complex Instruction Set Computer. CISC chip, for example
Motorola 68040 or Intel, provide many instructions to the Pentium
Programmers.
 RISC chips in comparison to CISC chips provide faster processing.
 Intel Corporation is the largest Micro Processor Manufacturing company in the
world.

Fundamentalsof Answer of the Check your progress :
Computers & 1. C.P.U.– An acronym for Central Processing Unit, is supposed to be the brain of
Information Technology
computer. It mainly executesthe programsand controlsdifferent partsof a com-
NOTES puter such as memory, input and output devices. Programs and data are stored
under itscontrol. It helpsyou see your output on the screen and get print out on
136 the paper through printer.
2. Central Processing Unit includes mainly 3 parts. They are as follows :
 Arithmetic & Logic Unit
 Main Memory Unit
 Control Unit
3. Control Unit–Control unit controls the internal process of a computer. It con-
trols the input and output processes of the computer. It also directs the ex-
change of data and instructions between memory and ALU.
4. Registers–Computer instructions are carried out by the C.P.U. To execute in-
structions, information is exchanged. C.P.U. of computers uses a memory unit
to exchange information fast and satisfactorily. This memory unit is called a
register. Registers are not the part of main memory. They store information for
time being. Size of a register equals to the capacity of its storage of bit.
5. Accumulator Register–This register stores the middle and last result of the
data being executed. Normally, these registers are used while execution of
information.
6. RISC stand for Reduced In Struction Set Computer and CISC stand for Com-
puter Instruction Set Computer.

EXERCISE

1. Explain central processing unit.
2. Describe the functions of control unit.
3. What are the two main components of CPU of a computer system ? List out the

main functions of each of these components.
4. What is an instructions set ?
5. What do you mean by registers ? Explain its different types.
6. What do you mean by processor speed ?
7. What are Arithmetic and Logic units ? What does it do ?
8. What do you mean by Logical Operations ?
9. What does memory buffer register do ?
10. What does Instruction Register do ?
11. Explain BUS.
12. What does System Clock do in a computer ?
13. Explain SISC and RISC.
14. Which types of processors are there in the market ? Explain.

9 Storage Devices Storage Devices
NOTES
The Chapter Covers :
137
 Introduction
 Storage and its needs
 Brain Vs Memory
 Storage Evaluation Units
 Data Access Methods
 Primary Storage
 Secondary Storage
 Hard Disk Operations
 Floppy Disk Drives
 Winchester Disk
 Optical Disk
 VCD
 CD-R
 CD-RW
 DVD
 Zip Drive
 Flash Drives
 Blu Ray Disk
 Memory Card
 Driving Naming Conventions In a PC
 Summary
 Exercise

INTRODUCTION

Storage device is one of the three parts of a computer. There are two types of storage
on a computer namely Primary and Secondary. Primary storage is of volatile nature and
secondary storage non-volatile. Volatile memory holds data temporarily; right from starting
computer till it shuts down. Either electricity goes or computer gets restarted somehow,
all data is lost. Non-volatile primary storage helps start your computer. It conatins some
very useful firmware to boot with computer. Booting is the process of starting computer.
Actually, this type of storage is called main memory. Secondary memory is what we use
to hold our data for a long period. We normally contain data that is of paramount
importance and also used for transfer. Secondary storage comes in different forms. Floppy
disk, Hard disk and Optical Disk are a few to name. This chapter focuses on all the storage
devices in a very friendly way.

Fundamentalsof STORAGE AND ITS NEEDS
Computers &
Information Technology When you are preparing for your exams the first thing you wish that you would remember
all what you read. Means you want to hold records what you have read previously.
NOTES Storage is something like a container where we want to store records of our work. Now
the question is how important this is. The answer lies with you. It is as important as
138 remembering our activities in our day to day life. In the real world, a man is supposed
to be suffering from a fatal brain disorder if he is unable to remember things. Likewise,
had computer been without its storage capacity , it would not have impressed the human
being today to this extent. Storage is one of the most exciting features of a computer.

Computers have more than one form of memory. We can generally classify them into
primary and secondary memory. Primary memory is used as a form of temporary memory
for calculation processes and storage of temporary values that need rapid access or updat-
ing, the contents of the primary memory disappear when the power is turned off. Primary
memory is important when executing programs. Bigger programs require more primary
memory. RAM(random access memory), Caches & buffers are just a few examples of
primary memory.

Secondary memory often comes in the form of hard disks, removable disk drives and tape
drives. Secondary memory is used for the storage of most of a system’s data, programs
and all other permanent data that should stay there, even when the power is turned off.
As a computer is fed with bigger, smarter programs and more data, it would naturally need
more secondary memory to hold them.

Storage comparison between computer memory and human brain
Humans are the creator of a computer. When we go through the anatomy of human
body, we find there is no difference between human body and computer system. Our
human body carries blood while computer systems carry electrons in their veins. There
are different parts of body and every part has its different functions. If you look at the
parts and observe carefully you will hardly find any difference in the structure of both.
Actually, this creation is totally based on our body structure. Similarly, computer memory
is based on our human memory system. You must have observed sometimes that you
easily grasp some of the telephone numbers and addresses and hardly forget them,
while some of them are hardly remembered. Similarly, like computers, we have options
to remember things temporarily and remember permanently. It is estimated that a
human brain can contain forty mega libraries where each mega library has a capacity
of eighty thousands of books on an average. It is surprising that average human minds
have a larger capacity to store data than a super computer. Some facts about the human
nervous systems are:
 In one second, the retina sends ten one-million-point images to the brain.
 By estimation, the brain has about 100 million MIPS worth of processing power

while a test super-computers only have a few million MIPS worth in processor
speed.
 The average brain can hold about 100 million megabytes of memory !!!
 Although the brain has got more ability, it has got more tasks to perform than
that expected from a computer. The brain has to constantly take charge of
maintaining the human body functions for the entire lifetime. It performs actions
like breathing, blinking, coordination of all the body parts are controlled
subconsciously by the brain all the time.
 Your ear drums pass sound information real-time at higher-than-CD-quality.
 In princple, the brain could be as quick as a computer in computational and
recording jobs.
 There are exceptional people who could read through a 500 page book in less
than an hour and remember all the contents as well as people who could
perform mathematical calculations at a snap of their fingers but they are only
rare examples that prove the hidden potential of the human brain.

STORAGE EVALUATION UNITS Storage Devices
NOTES
Computer memory is such a space where data are stored electronically as per instruc-
tions of the users. A unit called 'byte' is used to measure the amount of data and the
space available to store the data. Byte represents a letter, digit, symbol and white space
on the computer. For example, the word COMPUTER contains 8 letters. It means, the
word COMPUTER contains 8 bytes on computer memory. Apart from byte, memory
capacity is measured by some more units as depicted in Table 9.1.

Units Abbreviation Approximate Measure Actual Measure
( In bytes ) ( In bytes )

Kilobyte KB 1,000 (1 thousand) 1,024
Megabyte MB 1,000,000 (1 million or 10 lacs) 1,048,576
Gigabyte GB 1,000,000,000 (1 billion or 100 crores) 1,073,741,824
Terabyte TB 1,000,000,000,000 (1 trillion or 1 lac crores) 1,099,511,627,776

Table 9.1 : Measures of memory capacity

DATA STORAGE AND RETRIEVAL SYSTEM

There are two classifications of secondary or auxiliary storage devices based on the
data retrieval - Direct Access Storage or Sequential Access Storage.
Direct Access Storage
Direct access storage requires an input/output device that is directly connected to the
CPU; that is, it is said to be online, making the stored data available to the CPU at all
times. Such storage devices are called direct access storage devices.
An example of direct access media is a magnetic disk, such as the diskettes used with a
personal computer. It is easier to go directly to the file you want; it is as though you move
the record arm on your stereo directly to the song on the record you want to play instead
of having to listen to all the songs preceding the one you really want to hear. As men-
tioned, direct access storage is less expensive and has greater capacity than primary
storage; however, it is not nearly as fast.

Figure 9.3 : direct and sequential access 139

Sequential Access Storage
Sequential access storage is offline; the data in this kind of storage is not accessible to the
CPU until it has been loaded onto an input device. An example of sequential access media
is a reel of tape: Records are stored in sequence - alphabetically, one after the other. A
stack of punched cards is another example of sequential media.
A reel of tape can hold a great deal of data, which is perfect for many of a bank's purposes.
The problem, however, is that if you are looking for a customer name far into the alphabet
- Om or Manoj - you have to run the tape past all the earlier files first, a relatively slow
process.

Fundamentalsof Being outside the CPU and not directly connected to it, sequentially access storage
Computers & media is much slower than either primary storage or direct access storage. However,
Information Technology it has much greater-indeed, unlimited -capacity and is considered to be more secure
because it is stored off-line and isnot directly accessible to anyone who has gained
NOTES access to a computer's CPU. (See Figure 9.1)
Index Sequential Access
140 Index sequential access is a compromise between direct and sequential access methods
. In this, records are stored sequentially but the file where data are stored contains an
index. The index lists the key to each record stored and the corresponding disk address
for that record. The index works somewhat like the index in the back of a book. For
instance,suppose you have to find the room no. of Mr. R.P. Singh in a multi-storeyed
building having 1000 rooms - in a sequential method you need to start knocking each and
every room right from room no. 1 and would keep on knocking until you get it.

Employee Ad dr ess Ad dr ess Employee
Code Location Location Record

0001 1003 1001 0002 R.S. Patel
0002 1001 0002 0004 R.K. Rana
0003 1004 0003 R.P. Sinha
0004 1002 0004 N.P. Singh

Figure 9.2 : index sequential access

But, it may be the quickest and easiest through index method - just go to the index of
the building, look up the specific name i.e., Mr. R.P. Singh and room number given there
and then reach the right floor and right room. In the same way, data are retrieved on
a computer using index sequential method. Index sequential method is the best among
all the ways of access . It retrieves the data more quickly and more efficiently.

PRIMARY STORAGE

Memory is a working storage of computer. This is very important part of computer where
data, information and programs are kept during processing and are retrieved if needed.
Memory is also called primary memory or main memory. Memory uses some space for
storage that is definite in number called capacity or size of memory. The unit, that
measures capacity of memory is called byte. For instance, an ordinary personal computer
has a memory equal to 1 MB, means it can contain approximately 1048576 characters.

Computer memory is mainly of two types -

 RAM or Random Access Memory

 ROM or Read Only Memory

Random Access Memory

Random Access Memory is the same as main Figure 9.3 : Random Access
memory. RAM refers to a memory in which Memory
data and programs can not only be obtained
from primary storage, but also can be put into
it. It is volatile, means the contents of the
memory disappear once the current is turned
off. RAM is found in different sizes like 4 MB,
8 MB, 16 MB, 32 MB, 64 MB, 128 MB and so
on. (See Figure 9.3)

Several types of RAM are used in personal computers : Storage Devices
NOTES
 Dynamic RAM ( DRAM)
141
 Synchronous DRAM ( SDRAM )

 Static RAM ( SRAM )

Dynamic RAM - Dynamic RAM is abbreviated as DRAM. DRAM being the more
common type needs to be refreshed (Refreshing means recharging the chip with
electricity) more often - thousands of times per second. Each time the chip is refreshed,
the contents are lost. Recharging the chip quite often makes it slower than other RAMs.

Synchronous DRAM - This type of chip works faster than standard DRAM. The chip
is faster because it moves at the speed of CPU's clock. By running with the speed of
a clock, it can move data much more efficiently than DRAM.

Static RAM - Static RAM needs to be refreshed less often and hence contains data
longer than DRAMs. All of the RAMs are volatile but DRAM is slower and less
expensive than SRAM. It is especially used for special purpose computers.

Read Only memory

Read only memory, in short, ROM is a permanent Figure 9.4 : Read only
memory of computer. Programs are built into ROM memory
at the factory level and cannot be changed by the
user. You can read them, but can not alter. ROMs
are also referred as firmware because they contain
programs that are 'firm' - not changeable. ROM is
non-volatile - the contents do not disappear when
the current is turned off. (See Figure 9.4)
ROM is of the following types :

 Programmable Read Only Memory (PROM)

 Erasable Programmable Read Only Memory (EPROM)

 Electrical Erasable Programmable Read Only Memory (EEPROM)

Programmable Read Only Memory – Know as PROM is short, it is another kind of
firmware that can be programmed only once. They are like ROM, in that, the contents
cannot be altered. However, they are custom-made by the manufacturer to meet particular
customer needs and have the advantage of being able to operate faster than typical
application programs written in a high level language.
Erasable Programmable Read Only Memory – Shortly known as EPROM, it is like
PROM. Information stored on it can be erased in the presence of ultra violet rays and new
information or programs can be written.
Electrical Erasable Programmable Read Only Memory (EEPROM) – This is a new
technology EPROM, where electric current is used instead of ultra-violet rays.

RAM VS ROM

RAM, means Random Access Memory and ROM means Read Only Memory both are the
class of Primary Memory. When both are primary memories would there be no differences
between them. Of course, there would be. Let's know what are the differences between
RAM and ROM.
There are many differences between RAM and ROM which every computer literate person
must know. The following table shows the difference between the two :

Fundamentalsof Random Access Memory Read Only Memory
Computers & 1. This is the temporary memory of 1. This is the permanent memory
Information Technology
computer. of the computer.
NOTES 2. We keep writing and deleting the 2. In it, the data is written by

142 data in it. the manufacturer.
3. When the power goes out or of the 3. In it, the stored data doesn't

computer gets Shut down for any get deleted in any situation.
reason the stored data is deleted.
4. It is in several storage capacities. 4. It has nothing to do with the
storage capacity.
5. It starts working after the
computer is on. 5. It is used for switching ON
the computer.

Table 9.2 : Differences between RAM and ROM

CACHE MEMORY
In simplest terms, cache memory is a special type of high speed memory built onto or
next to the processor. Your processor moves and works with a lot of data. Sometimes,
your processor works on a problem and needs to set it aside and start working on another
before picking up the original problem. Without cache, your processor would have to store
the set aside data into conventional memory (RAM). While there is no particular reason
your processor cannot do this, setting data aside in conventional memory subjects the data
movement to the limitations of your motherboard and how fast it can move memory. It’s
nowhere near as fast as your processor. Designers figured out that there had to be a much
faster and more efficient way for this to happen.
Depending on what you do, the amount of cache your system has, can greatly increase
or decrease the overall speed of the system. For example a 450MHz Pentium III has lot
more cache than a 450MHz Celeron. Even though both chips have the same clock speed,
they do not perform at the same level in all situations. For data intensive applications like
complex spreadsheets or graphic design, the Pentium III will beat out the Celeron any
day. The lesson here is to know what you will be doing with your computer before you
settle on a processor. If you are into CAD design, and buy a Celeron, you may be sorely
disappointed. If, on the other hand, you just write letters and surf the Internet, you may
not want to spend the extra money on the Pentium III.
Types of Cache Memory
Types of cache memory are L1m L2 & L3.
L1 Cache : L1 cache is also known as onboard or primary cache and is built into the
CPU itself. L1 cache is typically very small in size (for most computers it is 16KB
although this is changing rapidly) but it is very fast.
L2 Cache : L2 cache is also known as external or secondary cache. It is built into a
separate chip, but it is still much faster than conventional memory because it, too, is not
subject to the speed limitations of the motherboard. Typically ranges for L2 cache are
128KB – 1MB.
L3 Cache : Usually, it is not used. This cache is connected to the motherboard. This cache
is used for computers with high capacity. L3 is not necessary for all computers.
L1, L2 & L3 all increase the processing speed of CPU. However, au three of these help
the CPU is different ways. L1 keeps the instructions being executed. L2 keeps the next
possible instruction and L3 keeps all the possible instruction.

SIMM Storage Devices
NOTES
A SIMM, or Single In-line Memory Module, is a type of memory module used for
random access memory in personal computers. It differs from a DIMM (the most
predominant form of memory module today) in that the contacts on a SIMM are
redundant on both sides of the module.
Most early PC motherboards (8088 based PCs and XTs) used socketed DIP chips. With
the introduction of 80286 based PC/ATs, which could use larger amounts of memory,
memory modules evolved from the need of saving motherboard space and to ease
memory expansion. Instead of plugging in 8 or 9 single DRAM DIP chips, only one
additional memory module was needed to increase the memory of the computer. A
few 80286-based computers used (often non-standard) memory modules like SIPP
memory (single in-line pin package). SIPP’s 30 pins often bent or broke during instal-
lation, which is why they were quickly replaced by SIMMs which used contact plates
rather than pins.

Figure 9.5 : A Single In-line Memory Module 143

The first SIMM appeared on the PS/2 in the mid 80’s, having been first proposed by
Skip Coppola while at IBM. It solved several problems of that time, including shrinking
motherboard real estate (they took up much less board space than socketed chips) as well
as the effects of rapidly advancing memory capacities (a motherboard would quickly
become obsolete based on its sockets for a particular RAM chip capacity) This also allowed
the manufacturer (IBM at this time) to source RAM chips from different vendors and in
different packaging, yet still allow them to be interchangeable through this intermediate
form (the SIMM).
The first variant of SIMM had 20 pins and it provided 8 bits of data (9 bits in parity
versions). Therefore, systems which required 30 pin SIMMs needed to be installed in sets
of 4 (because processors such as the 80486 had 32 bit data paths).
The second variant of SIMMs had 72 pins and provided 32 bits of data (36 bits in parity
versions). Around 1997, 72-pin SIMMs replaced 30-pin SIMMs.
Due to the differing data bus widths of the memory modules and some processors,
sometimes several modules must be installed in identical pairs or in identical groups of four
to fill a memory bank. For instance, on 80386 or 80486 systems (data bus width of 32
bits), either four 30-pin SIMMs or one 72-pin SIMM, was required for one memory bank.
On Pentium systems (data bus width of 64 bits), two 72-pin SIMMs are required.
The earliest SIMM sockets were conventional push-type sockets. These were soon re-
placed by ZIF (Zero Insertion Force) sockets in which the SIMM was inserted and rotated
until it locked into place. To install a SIMM, the module must be placed in the socket at
an angle, then rotated (angled) into position. To remove one, the two metal or plastic clips
at each end must be pulled to the side, then the SIMM must be tilted back and pulled
out. The earlier sockets used plastic retainer clips which were found to break, so steel clips
replaced them.

Fundamentalsof Standard sizes available in 30-pin SIMM are 256KB, 1MB, 4MB, 16MB whereas in 72-
Computers & pin SIMM are 1MB, 2MB, 4MB, 8MB, 16MB, 32MB, 64MB, 128MB
Information Technology
DIMM
NOTES
A DIMM, or Dual In-line Memory Module, comprises a series of random access
memory integrated circuits. These modules are mounted on a printed circuit board and
designed for use in personal computers. DIMMs began to replace SIMMs (single in-
line memory modules) as the predominant type of memory module as Intel’s Pentium
processors began to control the market.

Figure 9.6 : A Dual In-line Memory Module

The main difference between SIMMs and DIMMs is that SIMMs have a 32-bit data path,
while DIMMs have a 64-bit data path. Since Intel’s Pentium has (as do several other
processors) a 64-bit bus width, it required SIMMs installed in matched pairs in order to use
them. The processor would then access the two SIMMs simultaneously. DIMMs were
introduced to eliminate this inefficiency. Another difference is that DIMMs have separate
electrical contacts on each side of the module, while the contacts on SIMMs on both sides
are redundant. (See Figure 9.6)

SECONDARY STORAGE

Secondary storage, also called auxiliary storage, is found physically outside the processor.
This is a long-term, non-volatile memory. Though ROM is also non-volatile memory to
which data cannot be added. Besides storing data, secondary storage is also useful for
transferring them from one computer to another. Secondary storage devices are greatly
used in taking backup which can be used if any sort of disorder takes place on the
computer.

Types of Storage Devices

There are a number of secondary storage devices. They can broadly be classified into
Magnetic Tape, Magnetic Disk and Optical Disk.

Magnetic Tape

Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin
plastic strip. Nearly all recording tapes are of this type, whether used for video, audio
storage or general purpose digital data storage using a computer.
Magneto-optical and optical tape storage products have been developed using similar
concepts, but have achieved little commercial success.
Positive Aspects :

1. Is relatively less expensive.
2. Is used to store data in a large amount.
3. Is reliable, durable and transferrable. Is used to backup important data.
144

Negative Aspects : Storage Devices
NOTES
1. Has sequential data access methods, in which, to retrieve a particular data, one
has to pass through the entire data. Check Your Progress:
1. What is Dir ect Access
2. Its speed is low, the modification, search etc takes a lot of time.
St orage ?
Cartridge Tape 2. Namethe several types of

Most modern magnetic tape systems use reels that are much smaller than the old 10.5 RAM used in per sonal
inch open reels and are fixed inside a cartridge to protect the tape and facilitate handling. computer .
Many late 1970’s and early 1980’s home computers used Compact Cassettes encoded 3. What aretypes of ROM ?
with the Kansas City standard. Modern cartridge formats include LTO, DLT, and DAT/DDC. 4. What iscachememory ?

Tape remains a viable alternative to disk due to its lower cost per bit. Though the real 145
density is lower than that of disk drives, the available surface on a tape is far greater. The
highest capacity tape media are generally on the same order as the largest available disk
drives (about 1 TB in 2007.) Tape has historically offered enough advantage in cost over
disk storage to make it a viable product, particularly for backup, where media removability
is also important. The rapid improvement in disk storage density and price, coupled with
arguably less-vigorous innovation in tape storage, has reduced the market share of tape
storage products.

Magnetic Disk

Magnetic Disk is another form of sequential access storage, but it is far better for direct
access storage – which is not possible in magnetic tape. A magnetic disk can be of two
types :

 Hard Disk

 Diskettes or Floppy Disks

Hard Disk

A hard disk, Commonly known as a HDD (hard disk drive) or hard drive (HD) and
formerly known as a fixed disk) is a non-volatile storage device which stores digitally
encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking,
“drive” refers to a device that drives removable media, such as a tape drive or (floppy)
disk drive, while a hard disk contains fixed non-removable media. However, in recent
times, the hard disk has become more commonly known as the “hard drive”.

Hard disks were originally developed for use with computers. Today, applications for
hard disks have expanded beyond computers to include digital video recorders, digital
audio players, personal digital assistants, digital cameras, and video game consoles.
Mobile phones from Samsung and Nokia can be found with HDDs.

Pocket Hard Disk Drive

A pocket hard drive is a high capacity alternative to flash Figure 9.7 : Pocket
drives. Pocket hard drives couple traditional hard disk storage Hard Disk Drive
(allowing increased capacity over some flash drives) with con-
venient size and USB connections. Although these devices
are somewhat larger than flash drives, they are still conve-
nient for storing and transferring large amounts of data. Pocket
hard drives usually have a capacity of 4-8 Gigabytes. Till now
the Hard Disk drives of 400 GB's are available in the market.

Unlike flash drives and card storage, pocket hard drives retain the platter(s) and moving
head(s) of traditional hard drives. Because of these moving parts, pocket hard drives are
much less tolerant of abuse than flash-based technology, including Mini SD cards, Compact
Flash and thumb drives. Features such as USB connections, driver-less data access and
small size are present in virtually all pocket hard drives. (See Figure 9.7)

Fundamentalsof Role of Hard Disk
Computers &
Information Technology Hard disk plays an important role in the following important matters of a computer.
Performance – Hard disk plays an important role in the performance of the system.
NOTES The speed of PC booting is directly related to the speed of the hard disk. When multi-
tasking is in use, the performance of Hard disk is more important, or it is so when
146 a large amount of data, for ex. Graphics work. Sound or Video editing or database
work, is being processed.
Storage capacity – This is a special kind of performance. The bigger is the hard disk,
the more data and program will be stored in your computer.

Base casting holes to mount cover
Spindle holes to mount case
Slider (and head)
Actuator arm
Actuator axis
Actuator

Platters

SCSI interface Jumper Ribbon cable (which connects
connector head to the logic board)
Pins Jumper Power
connector Tape seal

Figure 9.8 : Different components of hard-disk

Software support – To load the new software peoperly a hard disk with more space
and faster speed is required. Previously, a hard disk of a few MB was enough. But
in today's PC, the hard disk of even 40 GB seems to be outdated and to load modern
operating systems many gigabyte harddisk is the minimum requirement.
Reliability – To measure the importance of any hardware item, it is enough to find
how difficult it would be if it stops working. On this scale, data can be more important
than any hardware item of a computer. A hardware can be changed, but data can't
be changed. A harddisk with good maintenance and backup tendency can save us from
the terrible situation of data getting demaged.

Hard Disk Operations

A hard disk uses a round and flat disks. It is called platter. On both of its side, there
is a coat of special media matter which is designed to store information in magnetic
pattern. Platterns are mounted after a hole is cut in the middle and is fixed on an
axis. Platter rotate at a high speed by a special motor attached to the axis. It contains
special magnetic read/write devices which are called heads. These are put on the
sliders and are used to record information on the drive or to read it. Sliders are put
on the arms which is mechanically a link. This device is called actuator. In it, the logic
board, controlls the activities of other sections and communicates with the rest part
of the PC.
Every surface of each platter of the disk can store 10 billion data separately. They are
arranged in a big chunk for convenience. Every platter has two heads, out of which

one is on the top and the other is in the bottom of the platter. Thus in a hard disk Storage Devices
of 3 platters, there are normally 6 surfaces and 6 total heads. The information of every NOTES
platter is recorded in concentric circle. These circles are called tracks. Each track is
divided into smell sections which are called sectors. Every sector contains almost 512 147
bytes of information.
The entire disk because of the miniaturization of its contents and the important role
of hard disk in PC, is manufactured with a high degree of Precision. The main part
of the disk is protected against the outer air, so that there are no containments on it
and there is no reason of read/write heads getting spoiled.
The first stpe to access a disk is to find out the part of the disc, on which the data
is to be viewed. Amidst them, Applications, Operating System, System BIOS and
possibly a special driver software of the disc decides, which part of the disc is to be
read. The location on the disk passses through more than one translation steps until
the last request is not made to the drive with address represented with respect to
geometry. The geometry of the drive is denoted, normally with respect to cylinder,
heads and sectors which the system wants to be read by the drive. For Addressing
purposes, the cylinder is equal to the track. On the disc drive interface, the disc is
given the address of the sector and is sent to read.
The control program of the Hard Disk sees whether the requested information is
available in the buffer or not. If it is available, control supplies this information without
viewing it on the disk. In most of the cases, the disk drive is already rotating. If it is
not so, the controller board of the drive activates the axis motor to rotate the drive
at the operative speed.
The controller board interpretes the address which it obtained for read and completes
additional translation steps which goes to the specific characteristics account of the
drive. The logic program of the Hard disk, again glances at the last number of the
requested cylinder. The cylinder number tells which track of the surface of the disk
is to be seen. Board actuator directs the read/write head to move towards an
appropriate track. When the head is in the right position, the controller activates the
head directed in the suitable read location. Head, after starting the reading of the
track, searches for the sector for which it has been instructed. It waits for the disk to
reach to that sector number and when it gets there, reads the contents of that sector.
The controller board combines the information flow of the hard disk in a temporary
storage area (buffer). Then sends that information on hard disk interface to satisfy the
request made for data to system memory.

Hard Disk Platters And Media

Every hard disk contains one or more flat disks, which are to store data in the drive.
These disks are called platters. These are made of two main things. First substrate
material of which most part of the platters is made and which provides structure and
hardness. Second, it has a magnetic media coat which contains the magnetic implulse
which represents data. The name hard-disk has been given to it, in fact, because of
the hardness of the platters which is in contrast to floppy disc and media which use
flexible platters. In fact, when the matter is flexible, one can't call them platter. Platter
in itself stands for something rigid.
It is platters that contain data record. Thats why the quality of platters and their media
coating is soft. The surface of every plattes and the hard disc is assembled in a neat
and clean room so that the platters get as little dirty as possible.

Platter Size

The platter size of the hard disk is the primary determinor of its entire physical sizes.
It is also called the form factor of the drive. Maximum drives are made into any one
of the various standard hard disk form factors. The disk is, at times, contexted by size
specification. For example, some people, will be found talking about 3.5 inch hard disk.
When this terminology is used, this, generally, refers to the form factors and normally,

Fundamentalsof form factor is based on the size of the platters. The size of the platters of the disk
Computers & is generally same for all the drives of the given farm factor, though, it is not always
Information Technology true. Particularly, it is not so with the new drive. Every platter of a particular hard disk
is of the same diameter.
NOTES
Number of Platters
148
In a hard disk, as per the design of Fig. 9.9 : Hard Platter
the hard disk, there may be one or
more platters. The standard user hard
disk, which is possibly fitted in your
PC, mainly use one to five platters.
Some high power drives which are
mostly fitted in a server, use almost a
dozen platters. In some old drives
even more platters were used. In
every drive, all the platters, to form
a single assembly are physically at-
tached to each-other on a central axis
which rotates as a unit. It is made to
rotate by spindle motor. Platters are
kept apart by using spaces ring which
is fixed above the spindle. The entire
assembly is protected from above by
using some screws and cap or cover.

Every platter has two layers which can store data. Every layer has a read/write head.
Normally both the surfaces of the platter is used, but it does not take place all the time.
Some old drives which use dedicated servo positioning keep one surface for servo infor-
mation. New drives don't need to keep one surface safe for servo information. But at
times, because of marketing, one surface is left without using it.

Magnetic Media

Today's hard disks use thin film media. As it is clear from the name itself, the thin film
media, has a thin layer of magnetic substance which is put on the layer of the platter. It
is called thin film media as it is thinner than the oxide media. To deposit media material,
a special production technique is used. The similar method is electoplating which uses a
process similar to that used in electroplatting ornaments. The second method is sputtering
which uses vapour deposition process taken from the creation of half-conductions to
deposit a very thin layer of magnetic metarial on the surface. In sputtered platters, the
surface is more lavelled and flat than that in plating. Because of the increasing requirement
of high quality on the drive, sputtering has become the primary method, which despite
its high prices, is used on new disk drives.

In comparison to oxide media, the thin film media is more uniform and smoth. It has very
refined magnetic properties which enable it to contain more data in the same amount of
space. Lastly, it is a substance harder and more durable than oxide, therefore there are
few chances of its damage.

After applying magnetic media, the surface of every platter is covered with a thin safety
layer of carbon. On all of these a very thin smooth layer is applied. This material is used
to protect the disk from heads or other external matter that can enter the drive and cause
sudden damage.

IBM researchers are working on an fascinating new matter which, in the coming years,
will replace the thin film media. In it, instead of sputtering a metallic film on the
surface, a chemical solution, which contains organic molucules and iron and platinum
particles, is coated on the platters. Then, this solution is expanded and heated. After
it, the iron and platinum particles automatically arrange themselves into a crystals grid

Storage Devices
NOTES

Figure 9.10 : 5.25" platter with thin film media (above) and 5.25"
platter with oxide media (below)

in which the crystal of each can contain the magnetic charge. IBM is going to name
this structure "Nanocrystal superlatice". This technique will increase the areal density
capacity of the recording media of the hard disk by 10 to 100 times. Of course, it
will take years and it will have to co-ordinate other areas of the hard disk, especially
that in the improvements in the read/write capacities. Still, it is amazing and shows that
a lot of improvement is required in magnetic storage.

Tracks and Sectors

Platters are arranged in specific architectures so that organised storage and retrieval
of data can be made possible. Every platter is divided into thousands of tracks which
are strongly adhering to the concentric circles. These are just like the annual rings of
trees.

Tracks store a lot of information which is not considered fit for the smallest storage unit
on the disk. Therefore, the track is further divided into secotrs. A sector is the smallest
unit of the stored information on the hard disk which can be individually addressed
and normally it stores 512 bytes of information. Earlier, the computer hard disk could
contain 17 sectors per track. Today, a hard disk can have thousands of sectors and the
use of zoned recording can allow more sectors on the big external tracks of the disk.

Hard Disk Tracks, Cylinders and Sectors

The information stored on the hard disk is recorded in tracks which are concentric
circles. It is based on the surface of each platter. Numbers are allotted to tracks, starting
from zero and moving from the external to the internal part of the disk. Every platter
of a modern hard disk, has thousands of tracks on it.

The head run by head actuator is moved
from internal to external part to access data.
This arrangement of data ensures easy ac-
cess to any part of the hard disk. It's why a
disk in called random access storage device.

Each track may contain thousands of bytes Figure 9.11 : Tracks on surface 149
of data. Making tracks the smallest unit of of Hard Disk
storage on a disk is a wastage, because,
even the small files will occupy large space.
Therefore, every Track is divided into rela-
tively smaller units called sectors. Every sec-
tor has 512 bytes of the user data, in addi-
tion, it has a few dozen of additional bytes
which are used in internal drive control,
finding errors and their rectifications.

Fundamentalsof Differences between Tracks and Cylinders
Computers & A hard disk is made of a number of platters in which each platter uses two heads to
Information Technology record and read the data. One head is for the top of the platter and the other is for
its bottom. The heads that access the platter are attached together on the assembly
NOTES of headarms. It means, all head move in and out at a time, so every track is physically
placed on a single track number. It is not possible at all that one head track number
is on 0 and the other is on 1000.
Because of this arrangement, the track location of heads is not called track number
but cylinder number. A cylinder is originally a set of all the tracks where all the heads
are located. Therefore, if one disk has 4 platters, normally it has 8 heads and the
cylinder number 720 (for example) will be made of a set of 8 tracks which will be
placed on track number 720 at the rate of 1 at each platter surface. This name comes
out of the fact that if you visualize these tracks mentally, they create a skelatal cylinder
as they are circles of the same size which are fixed as one on the other at the same
place.

Figure 9.12 : cylinder in a Hard Disk

For most of the practical purposes, there is not a major difference between tracks and
cylinders. It is like thinking about the same thing from different angles. The separate
sectors are addressed keeping in mind the context of the cylinder, head and sector. Since
a cylinder is a collection of the track numbers based on all the heads of the disk the sum
of specification track number and head number is equal to the sum of cylinder number
and head number which is same as the track number and head number.

Track Density and a Real Density

Normally, the track density is related to how solidly the tracks are tightened on the surface
of each platter. Every platter has the same track density. The track density of a disk will
be directly proportional to the information to be stored on the hard disk. Track density is
such a component of areal density which tells about the number of bits which can be
packed on the surface of the disk in each unit of area.
In the hard disk of the PCs, earlier there were only a few hundred tracks and they used
5.25" large form factor. farm factors, as a result the track density was a few hundred tracks
per inch. In the modern hard disk, there are tens of thousands of tracks and they can have
a density of 30, 000 or more tracks per inch.
The main obstacle in the way of increasing track density is to ensure that tracks don't
come close enough to each other, so that the head, in the reading of one track doesn't
take data from the adjacent track. To avoid this problem, the magnetic fields are
weakened in order that interference can be avoided, which to simplify other design
150 impact such as better read/write head technique and/or signal direction and use of
PRML methods to simplify signal direction and processing.