The document provides an overview of computer systems and their components. It describes how a computer system is made up of both hardware and software. The computer hardware is divided into five main sections - input devices, output devices, the system unit, secondary storage devices, and communication networks. Input devices such as keyboards, mice, and scanners allow users to enter data. Output devices like monitors and printers allow users to see or print data. The system unit contains the central processing unit (CPU), memory, power supply, and motherboard. Secondary storage devices include hard drives for long-term storage. Communication networks connect the various components.

1. CHAPTER TWO
Computer System
1

2. Introduction
• A System is any collection of component
elements (also called Subsystems) that work
together to achieve some objective (s).
• The components collectively make the whole
(the System).
• Each component has a specific task to
accomplish
2

3. Cont…
• A Computer is not a single machine.
• It is a System and the System contains lot of
subcomponents.
• A Computer System is made up of both hardware
and software.
• Software is another term for computer program.
Software is a series of instructions that tells a
computer what to do and how to do it.
• Hardware refers to the physical components of a
computer system
3

4. Computer hardware:
• The hardware of a computer system is made up
of a number of electronic devices connected
together.
• Elements of the computer hardware are
categorized in to five sections
 Input Devices
 Output Devices
 System Unit
 Secondary Storage Devices
 A communication network called Bus/Cables
4

5. 1. Input Devices
• An Input Device is any hardware component
that allows/enables users to enter data or
programs into a computer
• Input device converts data or instructions
from a form suitable to human beings to one
understandable by the computer
Example- Keyboard, pointing device (example:
Mouse), reading tools like Scanner and Digital
Camera
5

6. A. Keyboard
• It is an Input Device that contains keys users
press to enter data into a computer.
• Desktop computer keyboards normally consist
from 101 to 105 keys.
• These keys can be divided into five sections
1. Typing keys:-
– include English Alphabets A – Z, digits 0 -9, Enter
Key, Space, Backspace Key, Caps Lock Key etc. The
general use of typing keys is to enter characters.
6

7. Cont…
2. Computer keys
Keys like ‘Ctrl’, ‘Alt’, ‘Shift Keys’ etc.
 They are used usually in conjunction with other keys
3. Function keys
Keys labeled from F1 to F12.
These Keys perform different tasks based on the type of
software/program being used.
4. Numeric keys:-
These keys let you enter numerical data more easily
when you are working on number intensive tasks.
The numeric key contains mainly the numeric digits
keys (0 – 9), the four mathematical operators (+,-,*, /)
etc.
To use this section, the keyboard makes sure that the
NumLock key in your Keyboard is on
7

8. Cont…
5. Navigation keys / Cursor movement keys:-
• These are keys that are used to navigate
through your document.
• They are used to move pointers and/ or
cursors around the monitor screen.
• The following keys are very important
– Shift key
– Print Screen key
– Pause key
8

9. B. Pointing devices
• A Pointing device is an input device that
allows a user to control a pointer on the
screen.
a. Mouse- A Mouse is a pointing device that fits
comfortably under the palm of your hand
• It is the most widely used pointing device on
Desktop computers
• Mouse is used to move the cursor on your
computer screen, to give instructions to your
computer and to run programs and
applications.
9

10. Cont…
• It can be used to select menu commands, move
icons, size windows, start programs, close
windows etc.
• The most commonly used Mouse Actions are
– Click: - used to select an item.
• Click means press and release the Left Mouse Button.
– Right Click: - used to display a set of commands.
• Right Click means press and release the Right Mouse Button.
– Double Click: - used to open a document or a
program.
• Double means quickly press the Left Mouse Button twice.
10

11. Cont…
– Drag and Drop: - place the cursor over an item on
the screen and then press and hold down the Left
Mouse Button
B. Touch screen
• It allows the user to operate a computer by simply
touching the display screen
11

12. Cont…
C. Light pen- It uses a light sensor device to
select objects on a display screen.
• To select objects on the screen, a user presses
the Light Pen against the surface of the screen
or points the Light Pen at the screen and then
presses a button on the Pen
12

13. Cont…
D. Track ball:- Similar to a Mouse that has a ball
• A Track Ball is a pointing device with a ball on
its top.
• It looks like an upside-down mouse.
• To move the pointer you simply rotate the ball
with your thumb, fingers, or the palm of your
hand
13

14. Cont…
C. Reading Tools
• Some input devices save users time by
eliminating manual data entry.
• With these devices, users do not type or speak
into the computer.
• Instead, these devices capture data from a
source document, which is the original form of
the data. Because of these reasons they are
always called source data input devices.
• Some of these devices: Bar code reader,
Scanner, 14

15. Cont…
• A bar code reader is a device that can read
and interpret bar codes and input the data
into the computer
• Scanner is an input device that reads or scans
printed text, image, and pictures or graphics
and then produce a digital version of the
image so that it can be fed in to the computer
• Scanner is similar to a photocopier, except it
converts hard copy to soft copy.
15

16. • Mark and Character Recognition- are reading
tools that are able to recognize special
characters & marks.
• Example
– Magnetic Ink Character Recognition (MICR):-
– Optical Mark Recognition (OMR)
– Optical Character Recognition (OCR)
16

17. Cont…
• Magnetic Ink Character Recognition (MICR):-
– It is used by banks to automatically read those
unusual numbers on the bottom of checks and
deposit slips
– A special purpose machine known as reader or
sorter reads these numbers and provides input
that allows banks to efficiently maintain customer
account balances
• Optical Mark Recognition (OMR):-
• They read (determine LOCATION) of any pencil marks on
specially designed papers for this purpose.
• These devices are used to correct exam papers 17

18. Cont…
• Optical Character Recognition (OCR)-
– OCR devices are very special because they do
something more than scanning and that is they
will scan (read) pre-printed characters and convert
the data to a digital form and like the text editable
with a word processor program.
– OCR works like this
Text will be scanned
The page will be analyzed and here paragraphs
and different formats will be identified.
18

19. Cont…
• Each character will be checked with the set of characters
already existing with the
• Software to find a match.
• Whenever the match is found, the scanned
character will be replaced by the match, but if the
case is the opposite, then the software will take
some measure like:
• Replacing the character with no match by some
special character.
• Asking the user to enter by typing the
unrecognized character.
• Giving some suggestions and let the user to select
the real character
19

20. Cont…
D. Video Input Devices:
• Generally speaking these kinds of devices will
change video data into digital data and
eventually manipulated by the computer
• Example: -
• Digital Camera- Instead of film, a digital
camera uses a light sensitive screen at the
back of the camera
20

21. Cont…
E. Audio Input Devices- These devices help the
user to enter sound data in to the computer
systems.
– Example Microphone: - translates speech into an
electronic signal.
– Modern speech recognition software is able to
translate this into either commands or data.
– This enables the user to use a microphone as an
alternative to the keyboard
21

22. 2. Outputs devices:
• Output devices are used to get data either in
the form of softcopy or hardcopy.
• It is used to convert information from
machine-understandable form to a human
understandable form
Softcopy:-displayed on monitor, projector or
similar devices.
Hardcopy:-printed on paper.
A. Monitor: It displays visual information to the
user, and is therefore an output peripheral
device
22

23. Cont…
• Computer Monitors are the display devices
used to view the display output of a computer.
• The Technology of Monitors is rapidly
expanding. Now you can even connect
multiple monitors to a single computer.
• It consists of a display surface called Screen.
• Types of monitors:
– CRT Monitors
– LCD Monitors
23

24. CRT Monitors
• CRT Means “Cathode Ray Tube”, CRT monitor
has more lines of dots per inch, higher the
lines more amount of the resolution.
• It creates the picture by number of rows or
lines of the small tiny dots.
• Consider this Resolution 1024 x 768 resolution
will be sharper than 800 x 600 resolutions.
• It describes the technology inside an analog
computer monitor. e.g:-Desktop Computer
24

25. LCD Monitors
• LCD Monitors are called as “Liquid Crystal
Display”, It is an LCD Technology.
• Liquid Crystal Display consists of two sheets of
polarizing material with a liquid crystal solution
between them.
• When an electric current passed through the
liquid crystal solution, crystals align so that light
cannot pass through them.
• It is like a shutter either allows light to pass
through or blocking the light. e.g:-Laptop,
Calculator, clocks e.t.c.
25

26. Comparison between CRT and LCD
Monitors
• CRT Monitors are heavy and occupies more
space at the desk and the major weight of CRT
Monitors is due to heavy weight of Cathod Ray
Tube
26

27. Cont…
• Display Size of Monitor- Display size of a
monitor is calculated diagonally, the actual
display size is smaller.
• Consider 17" CRT monitor will actually have a
display size of only 16" inch Size
• CRT monitor comes in 15-inch to 21-inch sizes
(38 — 53 cm) and larger where as LCD
monitor: Display size of 17" LCD monitor will
have 17" Display size
27

28. • Resolution: - Every monitor supports up to its
maximum resolution.
• The actual display resolution you will get on
your monitor will depend on what maximum
resolution your graphics card can support and
what maximum display resolution your
monitor can display, whichever is lowest.
• Price: - CRT monitors are much cheaper than
LCD however they consume more power as
compared to counterpart LCD Monitor.
28

29. • Radiation Emission: - The radiation emissions
in CRT monitors are higher as compared to
LCD Monitors.
• Working on CRT Monitors for continuous long
hours may affect eyesight or cause head ache
• Advantages of CRT Monitors
– cost less
– Depths of colors displayed are much greater and
stronger
29

30. • Advantages of LCD Monitor
– size and weight
– do not have high radiation emission
– produce less eye tiredness to the user.
Plasma: - Plasma computer monitors are less
commonly used with computers due to their high
operating temperatures, high power consumption,
and fixed resolution.
30

31. B.Printer
• A printer is an output device that produces
text and graphics on a physical medium such
as paper
• Convert soft copy to hard copy
• Printers can be grouped into impact and non-
impact printers.
• An impact printer forms characters and
graphics on a piece of paper by striking a
mechanism against an ink ribbon that
physically contacts the paper.
31

32. • A non-impact printer forms characters and
graphics on a piece of paper without actually
arresting the paper.
• The printing speed of a printer is usually
expressed in pages per minute (ppm).
• Printer resolution is often expressed in dpi
(dots per inch)
• The larger the number, the higher the
resolution
32

33. • Advantages of printers include
– Information produced is permanent.
• Disadvantages of printers include
– The time to get the printout is slow, when
compared with display devices.
– Paper is wasted for obtaining the output.
– Printers are generally noisier than display devices.
33

34. 34

35. Daisy Wheel printer
• A daisywheel printer is an impact printer that
uses a wheel as a print head.
• As the wheel rotates, a hammer strikes the
backside of the spoke and presses it against
the paper to print a character.
• Advantages of a daisywheel printer
– Can print letter quality characters.
• Disadvantages of a daisywheel printer
– Printing speed is very slow.
– Cannot print graphics.
35

36. Dot-Matrix Printer
• A dot-matrix printer is an impact printer that
produces printed images with a print head
striking mechanism.
• Most dot-matrix printers use continuous-form
paper.
• A higher number of pins on the print head
means more dots are printed, which results in
higher print quality.
• The speed of a dot-matrix printer is normally
measured by the number of characters per
second (cps) it can print
36

37. • Advantages of dot-matrix printers
– Dot-matrix printers can print multipart forms.
– Dot-matrix printers can withstand dusty
environment, vibrations, and extreme
temperature.
• Disadvantages of dot-matrix printers
– Dot-matrix printers are generally noisy because of
the striking mechanism.
– Print quality of dot-matrix printers is not as good
as those from ink-jet printers and laser printers.
37

38. Line Printer
• A line printer is a high-speed impact printer
that prints an entire line at a time.
• The speed of a line printer is measured by the
number of lines per minute (lpm) it can print.
• Line printers are often used with mainframes,
minicomputers, or with a network in
applications such as manufacturing,
distribution, or shipping
38

39. Ink-Jet printer
• An ink-jet printer in a non-impact printer that
forms characters and graphics by spraying tiny
drops of liquid ink onto a piece of paper.
• Ink-jet printers can produce letter-quality text
and graphics in both black-and-white and colours.
• Some ink-jet printers can print photo-quality
images on any type of paper.
• Printer resolution is measured in dots per inch
(dpi).
• The speed of an ink-jet printer is measured in
lines per minute (lpm).
39

40. Cont…
• Advantages of inkjet printers include
– Inkjet printers are generally quiet.
– Inkjet printers can produce high quality colour output.
• Disadvantages of inkjet printers include
– Specialized papers are required to produce high
quality colour output.
– The ink cartridges and specialized papers are
expensive.
– The ink may smear when printed on ordinary paper
40

41. Laser Printer
• The mechanism of how a laser printer works is
similar to a photocopier.
• Laser printers are also known as page printers
because they process and store the entire page
before they actually print it.
• Most laser printers today can print text and
graphics in very high quality resolutions, ranging
from 600 dpi to 1200 dpi.
• Laser printers can print text at speeds of four to
over thirty pages per minute.
41

42. • Advantages of laser printers include
– Laser printers are generally quiet and fast.
– Laser printers can produce high quality output on
ordinary papers.
– The cost per page of toner cartridges is lower than
other printers.
• Disadvantages of laser printers include
– The initial cost of laser printers can be high.
– Laser printers are more expensive than dot-matrix
printers and ink-jet Printers. 42

43. Plotter
• A plotter is a large printer that generates high-
quality documents by moving ink pens over the
surface of a page.
• Plotters are particularly useful to engineers and
architects, as they produce high-quality
blueprints, maps, and floor plans.
• Two basic types of plotters are pen plotters and
X-Y plotters.
• Advantages of plotters include
– Can print on large printers.
– High quality printing
43

44. 3. System Unit
• A System unit also known as a Base unit is the
main body of a desktop computer.
• Inside of the system unit, there are a number
of components. Some of them are:-
• Memory, CPU, Motherboard, Power supply,
Cooling Fans, Internal disk Drivers,Expansion
cards and Slots.
•
44

45. 45

46. A. Power supply:- the Pc power supply converts 120/240
volts alternating current (AC) into 5/12 volts Direct
current(DC) used by the PC.
• The PC power supplies have built-in power on/off
switches and power connects for the motherboard and
the disk drives.
B. Motherboard
• It is the Main circuit board in system unit
• It Contains adapter cards, processor chips, and
memory chips
• Another name of mother board is called system board
46

47. C.Ports:- Port is used to connect external devices to
system unit.
• It is available in one of two genders which are male
and female.
• It is classified as Serial port and parallel port.
• Serial port: - is a Transmits one bit of data at a time.
• It connects slow-speed devices, such as mouse,
keyboard, and modem.
• Parallel port: - is connects devices that can transfer
more than one bit at a time, such as a printer and Disk
Drivers.
47

48. • Special-purpose port: - Allow users to attach
specialized peripherals (digital video cameras,
color printers, scanners, and disk drives) or
transmit data to wireless devices.
• For example: - FireWire port, MIDI (Musical
Instrument Digital Interface) port, SCSI (small
computer system interface) port, IrDA
(Infrared Data Association) port, and
Bluetooth TM port
48

49. D. Expansion slot and Card
• Adapter card: - is used to enhance system unit or
provides connections to external devices called
peripherals.
• Adapter card is called an expansion card.
• An expansion slot: - is an opening, or socket on
the motherboard that can hold an adapter card
with Plug and Play.
• The computer automatically configures cards and
other devices as you install them.
49

50. E. Central Processing Unit:
• To process, the computer needs two components, the
central processing unit & memory.
• The processor (CPU) is the one that actually process &
memory is needed to store the data & instructions
currently used by the CPU.
• The CPU (Central Processing Unit) or processor is a
microprocessor chip (a silicon chip with complex with
complex circuits) found on the motherboard.
• The mothered is the main board located inside the
system unit containing the different chips of the
computer.
50

51. • All computer operations are under the control
of the CPU, which has the following functions:
– It controls the transmission of data from input
devices to memory
– It processes the data held in main memory
– It controls the transmission of information from
main memory to output devices etc.
The CPU has got three main components: The
Control Unit, Register & Arithmetic Logic Unit
(ALU).
51

52. • Control unit (CU)
• It controls the flow of data & instructions
between the CPU & Memory, between the CPU &
Input/ Output devices, etc.
• It is responsible for loading, interpreting the
individual instructions that comprise the
computer program.
• The control unit also has the task of getting the
data needed by the instructions and returning the
result of the processing after the instruction has
been executed.
52

53. • To summarize tasks carried out by a CU are
listed below:
– decoding the instructions within a computer
– sequencing the reading and writing of data within
the CPU and externally on the data bus
– controlling the sequence in which instructions are
executed
– controlling the operations performed by the ALU
53

54. • Arithmetic –Logic Unit (ALU)
• The ALU is responsible for carrying out
arithmetical and logical operations like
addition, subtraction, comparison etc.
• CPU Register
– The CPU also contains a small high speed memory
which is used to store temporary results and
control information. This memory consists of a
number of registers, each performing a specific
function. Example:-
54

55. • Registers and functions
55

56. 56
F. Memory : is the work area of our computer
system. There are two categories of memory:
Primary and Secondary.
• Secondary Memory: - Consists of the various
devices that are able to store data & programs
even when the power is off. Example Hard drives,
Floppy Drives, CD & DVD etc…
• Primary Memory: - is the memory that is
intimately/closely associated with the actual
working of the computers. This includes memory
that holds the start up routines as well as the
current program & data it is working with. Mainly,
there are two types of primary memory.

57. I.RAM (Random Access Memory):- RAM is a
memory mainly used to store instruction and data
currently used by the central processing unit.
• As a result, it is called working storage. And this
memory has a direct relationship with the ALU
and CU, which are components of the central
processing unit.
• RAM is a memory that is logically divided into
many equal sized cells called memory locations.
Memory locations will be accessed using their
addresses.
57

58. • Properties of RAM:
– RAM is volatile, i.e. any data on RAM will be lost
when power is turned off.
– It is a read write memory. We can ‘read’ (retrieve)
data from RAM and again we can ‘write’ (store)
data in to RAM.
– It is up gradable
– It can be randomly accessed: You can access any
byte without touching preceding bytes.
58

59. II. ROM (Read Only Memory):- ROM is a memory used to
store critical instructions that are used to boot (start) the
computer.
• Data on ROM is etched/ fixed when it is fabricated and
because of this ROM sometimes is referred as firmware,
which means between the hardware and software.
Characteristics of ROM
• It is non-volatile. Data stored on ROM will not be lost
when the power is interrupted
• It is read only memory: that is we can ‘read’ (retrieve)
data from ROM but we can not ‘write’ (store) data in to
ROM. Data on the ROM can not be deleted or modified,&
that is why it contains the boot up instructions.
• It can be randomly accessed
59

60. 4.Storage devices (Secondary Storage
Devices)
• there are two types of storage devices
– secondary and
– primary storage devices.
• The need of secondary storage devices is that to store data
permanently.
Different types of memories can be compared and evaluated
on the basis of the following properties.
• Access Type: There are two types of accessing data from
secondary storage devices: sequential and random.
– sequential access means to access a particular data; you need to
go through the, preceding data before reaching to the required
data.
– In the case of random access, any random access any data can
be accessed randomly without considering the preceding data.
– A storage device that has fast access type (direct access type) is
preferred.
60

61. • Storage capacity: It refers to the capacity of the
devices to store data. It is measured in bytes {usually
with prefixes Kilo byte, Mega Byte, Giga byte etc.
• Removable: This one is about whether they are
removable (meaning can be carried and moved easily)
or not. There are some secondary storage devices that
are needed very much because of this property even if
they can store fewer amounts of data and they are
slow.
• Notice: Secondary storage devices can be classified
based on different criteria. For example based on their
portability, we can classify them as External & Internal
and based on the Technology they used Magnetic &
optical Storage devices.
61

62. • Secondary Storage Technologies: Broadly, we do have
two types of storage technologies:
– Magnetic storage
– Optical storage
• Magnetic Storage Principles:
– The basic science applied here is electromagnetism.
– Electromagnetism is about the relationship between
magnets and electricity.
– As transistors become on or off to represent 1 and 0 (bits) in
memory, bits are represented on magnetic storage devices by
magnetizing very tiny iron particles found on the media.
– The data storage media of magnetic devices is coated with
magnetically sensitive material like Iron oxide. And these
small tiny iron particles will be magnetized by the current
passing through the read-write head and aligned in some
fashion.
– They can wait magnetized and aligned whenever there is no
electric power and that is why they are permanent storage
devices.
62

63. I. Magnetic Storage Devices
• There are lots of devices that use basically this
principle to store data even if they are totally different
in different aspects to each other.
A. Magnetic Tapes
– Magnetic tapes are magnetic storage devices which are
the cheaper ones and are slower than the other magnetic
storage devices. They are slow because their data is
accessed sequentially: meaning each and every preceding
data before the needed one should be traced before
getting to the particular data. But at the same time they
are very cheap. With a low cost, you can have high storage
capacity.
– Users are discouraged to use magnetic tapes to store data
which is needed frequently. Thus, magnetic tapes are not
common to end-users.
– But they have advantages:
i) They are used to store data which is not needed frequently.
ii) They could be used as a back up storage devices.
63

64. B. Magnetic Disks
• Magnetic disks can be accessed randomly and are faster
than magnetic tapes. And there are different types:
• Floppy Disks (diskettes):
– These are removable storage devices
having a small size and you need to
have a floppy drive to use them.
– A floppy drive is the one that reads and writes data on the
floppy disk.
• Some of the components:
– Shatter: is used to protect the data access area from the
external environment. If there is any disturbance (may be
dust), then there will be a data loss.
– The Data Access Area: when the drive reads and writes
data, then the data access area is the area where the read-
write head scans the actual data medium, which is the
magnetic film.
64

65. – Hub: when inserting the disk to the disk drive, the hub will
be fit to the drive spindle and the disk can be spin.
– Label: This one is used just to write labels for the disk to
distinguish it from other diskettes.
– Write-Protect Notch: is a hole used to make the floppy
disk read-only. If it is open, data can not be recorded and
the diskette is said to be write-protected. It is possible to
open or close the notch by sliding a cover which is found
with the hole.
– Magnetic Film: this is where data can be read or recorded.
Usually this magnetic film is coated with iron oxide.
The Floppy Drive:
• The floppy drive is the one where you inserted your
diskette. When inserted, there is a mechanical part
that will open the shatter and make the data access
area exposed to the read-write head. And then the
read-write head will move over the magnetic film as it
spins and read or write data on it.
65

66. • Tracks and Sectors: A formatted floppy is
different from unformatted one by one major
thing: the presence of tracks and sectors on the
magnetic film. A formatted floppy (as a result it is
ready to be used) has its magnetic film divided
into thin concentric circles called track and each
track is again is divided into sectors. The floppy
drive will not be able to read and write data on
the magnetic film unless and otherwise the film
has tracks and sectors.
66

67. • Hard Disks (Hard Drives):
• Hard disk is a set of magnetic disks which are mounted
together and covered by a rigid '. Here the read-write head,
the disks and the drive are sealed together. That is why
these sometimes called hard drives.
• A hard disk is placed inside the system unit in micro
computers. It is not removable. Hard disks have also tracks
and sectors.
• Hard disks are very important since they have high storage
capacity and are faster.
• They could have a storage capacity if 40GB-160GB. Imagine
what we mean by 1 GB: 1 byte = 1 character
• 1 KB = 1024 bytes = 1024 characters
• 1 MB = =1024 KB = 1048576 characters
• 1 GB = 1024 MB = 107341824 characters.
67

68. • The weak part of the hard disk is that it is not
removable. Actually as we have seen before,
there are other magnetic disks called floppy
disks which are removable but with low
storage capacity. To solve this problem,
removable hard disks are invented which can
hold up to 2GB. Example: Zip drive.
68

69. Optical Disks
• Optical disks are always removable. On the surface of an optical
disk (an aluminum coated by plastic) high-power laser beam will
bum very small points (called pits) and a less power would be used
to read the surface by scanning the disk.
A. CD-ROM (Compact Disk Read Only Memory)
They have high storage capacity (up to 700 MB). CD-ROM drives will
read data, but will not write. The data will be there when they are
manufactured. Many application programs are coming stored using a
CD-ROM.
B. CD-R (CD-Recordable-WORM) {Write Once Read Many)
• This is a blank CD and data is going to be recorded by a peripheral
device called CD burner or CD writer. Data could be recorded by CD-
R only once which means data could not be erased and replaced by
another one. That is why they are called WARM (Write Once Read
Many).
C. CD-RW (CD-Rewritable)
• These types are erasable or recordable many times. There are also
coming high speed optical disks called D VD-ROM with the same
size like CD- ROMS but have higher storage capacity.
69

70. The capacity of Storage media is measured by the amount of
bytes it can hold.
70
StorageTerm Approximateno.of Bytes ExactNumberBytes
Kilobyte(KB) 1thousand 1,024or210
Megabyte(MB) 1million 1,048,576or220
Gigabyte(GB) 1Billion 1,073,741,824or230
Terabyte (TB) 1Trillion 1,099,511,627,776or240
Pet byte(PB) 1quadrillion 1,125,899,906,842,624or250
Exabyte(EB) 1quintillion 1,152,921,504,606,846,976or260

71. Computer Software:
• Software is a set of programs that instruct the
computer to perform a certain action. Software
is a sequence of electronic instructions that tells
the computer how to do certain tasks.
• A sequence of instructions used to carry out
some task is often called a program.
• When a computer is using a particular program, it
is said to be running or executing the program.
• The one who writes those programs is known as a
programmer.
• Computer software is divided in to two broad
categories:- System software and Application
soft ware
71

72. System software
• System software primarily exists for the computer
itself. System software consists of instructions or
programs that are used to manage the hardware
resources of a computer.
• It placed between the hardware and the
application software. I.e. it is used as an
intermediate for the communication between the
hardware and the application software of a
computer system.
• The system software can be of the following type:
1. Operating system software and
2. System development software (Language software)
72

73. 1. Operating system software
• Operating system is a set of programs that
controls and supervises the overall operation of
the computer.
• All computers require the OS. Operating systems
have the following functions in common:
– It manages the computer resources
– It interprets and processes commands
– It activates input/output devices
– It allows the system to understand application
software
– It schedules jobs
73

74. 2. Language software
• The other sub-division of the system software
is the system development software (the
language software), which are used by the
programmers to develop application
programs.
• System development software (language
software) includes the computer
programming language translators that are
used to convert written programs in to
machine language for execution.
74

75. • the major language software, namely the
compilers, assemblers and Interpreters, that
serve as translators
• programming languages: A language is a
systematic set of rules for communicating ideas.
A programming language is a series of commands
and codes that are used by the programmers to
develop a set of programs called software.
• Each programming language uses a set of
symbols that have a special meaning. Each
language has its own set of rules, called syntax.
• A program is a set of instructions that directs a
computer to perform certain tasks and produce
certain results.
75

76. 2. Application software
• Application software is a type of software that placed
between the user and the system software and allows
the user to perform a certain activity- such as creating
a document or editing a graphic image.
• They are also called application packages.
• Some important kinds of application software are:
– Word processing programs (Ms Word)
– Spreadsheet software (Ms Excel)
– Database management Presentation programs (Ms Access)
– Graphics programs
– Networking software
– Web designing tools and browsers
– Internet applications
– Communications programs Utilities
– Entertainment and education Multimedia authoring
Application Software 76

77. Question?
77