chapter 2.pptx

Chapter 2
Introduction to Computer System
 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. 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.
Introduction to Computer Applications

Chapter One: Introduction to Computer Chapter Two: Computer System Chapter Three: Number Systems
Computer hardware
 The hardware of a computer system is made up of a
number of electronic devices connected together.
 It is composed of a number of interacting physical parts
based on the need of the information.
Generally, the basic elements of the computer hardware
are categorized in to five sections. These are:
) Input Devices
) Output Devices
) System Unit
) Secondary Storage Devices
) Communication network called Bus/Cables, which links all the
elements of the System and connects the System to the external
world.

Computer hardware: 1. Input Devices
1
Keyboard
It is the most familiar 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.
A.Typing keys: These 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.
B.Computer keys: Keys like ‘Ctrl’, ‘Alt’, ‘Shift Keys’ etc. They are
used usually in conjunction with other keys.
C.Function keys: Keys labeled F1, F2, F3... F12 are Functional Keys.
These Keys perform different tasks based on the type of software/program
being used.
D.Numeric keys: The numeric key contains mainly the numericdigits
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.
E.Navigation keys / Cursor movement keys: These keys are usedto
navigate through your document, used to move pointers and/ or cursors around the
monitor screen.

Cont..
Keyboard
The following keys are very important:
 Shift keys are used to type capital characters when you are
working with small letters and special characters labeled on the
keys such as
 ?, !, @, &, #, $, , etc.
 Print Screen key is used to print a paper copy of whatever is on
the screen when the key is pressed (if a printer is attached).
 Pause key temporarily suspends an activity, pressing the
pause key once stops the activity, pressing any typing key
(except shift, caps lock) resumes the activity.

Cont..
2
Pointing devices
A Pointing device is an input device that allows a user to control a pointer
on the screen.
The following sections discuss the Mouse and other pointing devices.
A.Mouse: The Mouse is the most widely used pointing device on
Desktop computers. Mouse is used to move the cursor on your
computer screen.
The most commonly used Mouse Actions are: Click, Right Click,
Double Click, and Drag and Drop.
B.Touch screen : It allows the user to operate a computer by simply touching
the display screen. Example of a Touch Screen includes, ATM at a bank.
C.Light pen: It uses a light sensor device to select objects on a display
screen.

Cont..
Pointing devices
D Track ball:
Similar to a Mouse that has a ball. A Track Ball is a
pointing device with a ball on its top.
Tracker Balls have an advantage over the mouse that
a flat surface is not required for its operation and
does not require much space because the device is
stationary.

Cont..
3
Reading Tools:
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 thesedevices:
A Bar code reader: A bar code is a pattern of vertical lines/ vertical zebra-
striped marks in which the spacing and thickness can be used to represent
data.
B Scanner: 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.

Cont..
Mark and Character Recognition: devices able to recognize special
characters & marks, essential tools for certain application. These are:-
3
 Magnetic Ink Character Recognition (MICR):- It is used by banks to automatically
read those unusual numbers on the bottom of checks and deposit slips. to check
customer account.
 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.
 Optical Character Recognition (OCR):- OCR devices are very special because
they do something more than scanning. OCR works like this:
 Text scanned and 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 not,
the software will take some measure like: Replacing the character with no match by some
special character.

Optical Mark Recognition (OMR)
They are used to read questionnaires,
multiple choice examination paper in the
form of shaded areas. Optical character recognition (OCR) technology is a business solution
for automating data extraction from printed or written text from a
scanned document or image file and then converting the text into a
machine-readable form to be used for data processing like editing or
searching.

Video Input Devices
These kinds of devices will change video data into digital data. There are
always video cards involved. Example: - Digital Camera. Digital Camera: It
uses a light sensitive screen at the back of the camera. A small computer
inside the camera converts the pattern on the screen into a standard
graphics file which can then be transferred to a computer.
Audio Input Devices:
These devices help the user to enter sound data in to the computer
systems. Example Microphone.
Microphone: A 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.

HW Component: 2. Output 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.

HW Component: 2. Output devices:
1
Monitor
It displays visual information to the user, used to view the output of a
computer. There are three types ofmonitories:-
A.CRT Monitors: - CRT Means “Cathode Ray Tube”, CRT monitor has more
lines of dots per inch, higher resolution. It creates the picture by number of
lines of the small tiny dots. Consider this Resolution 1024 x 768 will be
sharper than 800 x 600 resolutions. e.g:-Desktop Computer
B.LCD Monitors: Liquid Crystal Display that it is like a shutter either allows
light to pass through or blocking the light. e.g:-Laptop, Calculator, clocks
e.t.c.
C.Plasma: - These monitors are less commonly used with computers due to
their high operating temperatures, high power consumption, and fixed
resolution.

Cont..
Advantages of CRT Monitors
) The primary advantage CRT hold over LCD is their color rendering,
contrast ratios. Depths of colors displayed are much greater and
stronger. CRT Monitors cost less as compared to LCD Monitors of
equivalent size.
Advantages of LCD Monitor
) The biggest advantage of LCD monitors is their size and weight.
LCD monitors do not have high radiation emission. LCD screen also
tend to produce less eye fatigue to the user.

Cont..
Printer
Produces text and graphics on a physical medium such as paper.
Printed information is often called hard copy because the information
exists physically
Printers can be grouped into impact and non-impact printers.
) Impact printer forms characters and graphics on a piece of paper by striking
a mechanism against an ink ribbon that physically contacts the paper.
) Non-impact printer forms characters and graphics on a piece of
paper without actually striking 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.

Cont..
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.

Cont.
.
The following types of printers will be considered in more
detail:-

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.

System Unit
The next fig. shows the components of system unit:

Cont..
2
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.
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
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.

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

Cont..
Expansion slot and Card
Expansion card (Adapter card :) - is used to enhance
system unit or provides connections to external devices
called peripherals.
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.

Cont..
Central Processing Unit (CPU)
To process, the computer needs two components, CPU & 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 or
processor is a microprocessor chip (a silicon chip with complex circuits)
found on the motherboard.
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 three main components: CU, Register &ALU.

Cont..
A 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.
 It has the task of getting the data needed by the instructions
and returning the result of the processing after the instruction
has been executed.
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

Cont..
B Arithmetic –Logic Unit (ALU)
The ALU is responsible for carrying out arithmetical and
logical operations like addition, subtraction, comparison etc.
C CPU Register:
It 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:-
) Instruction Register:- Holds a copy of current instructions
) Program Counter:- Points to the next instruction to be executed in
memory
) Data Register:- Used for store data to be executed temporarily

Cont.
.

Cont..
6
Memory
 The work area of our computer system. There are two
categories of memory: Primary andSecondary.
 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: intimately associated with the actual
working of the computers. there are two types of primary
memory.
 1 RAM
 2 ROM

Cont..
RAM
 Used to store instruction and data currently used by the CPU. As a result, it
is called working storage.
 It has a direct relationship with the ALU and CU, which are
components of the central processing unit.
 Logically divided into many equal sized cells called memory locations.
Memory locations will be accessed using their addresses.
Properties of RAM:
) It 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.

Cont..
2
ROM
Used to store critical instructions that are used to boot (start) the
computer.
Data on ROM is etched 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 a 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

Secondary Storage Devices
It needs to store data permanently.
Factors that determine secondary storage devices:
I: Access Type: There are two types of accessing data from secondary storage devices:
sequential andrandom.
) Sequential access means to access a particular data; you need to go through the preceding
data before reaching to the required data.
) Random access any data can be accessed randomly without
considering the preceding data.
II: Storage capacity: the capacity of the devices to store data. It is measured in bytes, Kilo
byte, Mega Byte, Giga byte, etc.
III: Removable: About whether they are removable or not.
Notice: Secondary storage devices can be classified based on different criteria.
Eg. based on their portability, as External & Internal and based on the
Technology they used, Magnetic & optical Storage devices.

Secondary Storage Technologies
Broadly, two types of storage technologies:
I. Magnetic storage
II Optical storage
I. Magnetic Storage
Magnetic Storage Principles: 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.

A. Magnetic Tapes
The cheaper ones and are slower than the other magnetic storage devices.
They are slow because their data is accessedsequentially.
Users are discouraged to use magnetic tapes to store data which is needed
frequently. Thus, magnetic tapes are not commonto
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.
B. Magnetic Disks
Magnetic disks can be accessed randomly and are faster than magnetic tapes.
And there are different types:

Floppy Drive
removable but with low storage capacity
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.
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.
Hard Disks (Hard Drives)
Hard disk is covered by a rigid.
Here the read-write head, the disks and the drive are sealed together.
That is why sometimes called harddrives.
A hard disk is placed inside the system unit in micro computers. It is not
removable . Hard disks have also tracks andsectors.
Very important since they have high storage capacity and are faster.
The weak part of the hard disk is that it is not removable. To solve this
problem, removable hard disks are invented which can hold up to 2GB. Eg:
Zip drive.

II Optical disks: they are always removable.
A. CD-ROM (Compact Disk Read Only Memory:)
They have high storage capacity (up to 700 MB). It will read
data, but will not write.
The data will be there when they are manufactured.
B. CD-R (CD-Recordable-WORM) (Write Once Read Many)
Data could be recorded by CD-R only once, but not be erased and
replaced. That is why they are called WARM (Write Once Read Many).
C. CD-RW (CD-Rewritable)
They are erasable or recordable many times.

Cont..
The capacity of Storage media is measured by the amount of bytes it can hold.
Storage Term Aproximate no.of Bytes Exact Number Bytes
Kilobyte 1Thousand 1024 or 210
Megabyte 1 Million 1,048,576 or 220
Gigabyte 1 Billion 1,073,741,824or 230
Terabyte 1 Trillion 1,099,511,627,776 or 240
Petbyte 1 Quadrillion 1,125,899,906,842,624 or 250
Exabyte 1 Quintillion 1,152,921,504,606,846,976 or 260

Bus/Cable
 It carries data communication between the
major components of the computer, including
the microprocessor.
 Not all of the communication that uses the bus
involves the CPU.
 The system bus consists of three different
groups of wiring:
I. Data bus,
II. Control bus, and
III. Address bus.

Control bus
It carries the signals which can be sent from the CU within theCPU.
Different architectures result in differing number of lines as each line is used to perform a specific
task. For instance, different, specific lines are used for each of read, write and reset requests.
Data Bus
Used for the exchange of data between the processor, memory and peripherals, and is bi-
directional
the number of wires used in the data bus (sometimes known as the ’width’) can differ. As such, a
greater width allows greater amounts of data to be transferred at the same time.
Address bus
It contains the connections between microprocessor and memory, the locations that the CPU is
reading from or writing to.
Its width corresponds to maximum addressing capacity of the bus.
The addresses are transferred in binary format, address capacity is equal to two to the power of
the number of lines present (2lines ).
Control bus
Data Bus
Address bus

Computer software
Software is a set of programs that instruct the computer to
perform a certain action.
a program is a sequence of instructions used to carry out some
task or to perform certain tasks.
Computer software is divided in to two broad categories:-
1 System software and
Application software
2
1
System software
primarily exists for the computer itself.
It 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. The system software can be of the following type:
AOperating system software and
BSystem development software (Language software)

 Operating system software
 It is a set of programs that controls and supervises the overall operation of
the computer.
 All computers require the OS, common functions:
 ) 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
 Language software
 Used by the programmers to develop application programs.
 Includes the computer programming language translators that are used to convert
written programs in to machine language for execution, namely the compilers,
assemblers and Interpreters.
 Each programming language uses a set of symbols and codes that have a special
meaning which used by the programmers.
 Each language has its own set of rules, called syntax.

2
Application 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

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