Introduction to computers

Compiled by : S. Agarwal, Lecturer & Systems Incharge, St. Xavier's Coll

Study Note developed by
S. Agarwal,
Lecturer & Systems Incharge ,,
St. Xavier’s Computer CentreSt. Xavier’s Computer Centre
St. Xavier’s CollegeSt. Xavier’s College
KolkataKolkata
July-2002

What is a computer ?
A computer is an electronic
device capable of performing
arithmetic and logical
operations. It can also store a
large volume of information.

Arithmetic operations involve the
general mathematical calculations like
addition, subtraction, multiplication and
division.
Logical operations involve comparisions
like > < = etc.

How does a computer work?
INPUT  PROCESS  OUTPUT
INPUT consists of DATADATA & INSTRUCTION.INSTRUCTION.
PROCESS is a set of instructions stored in the
computer to carry out the instructions given by
the user. The process is also called a
PROGRAM.
OUTPUT is the set of results generated after
processing the Input.

DATA & INFORMATION
DATADATA is described as some FACTS, FIGURES
and STATISTICS about a particular instance.
For example : MARKS in individual subjects.
INFORMATIONINFORMATION is some FACTS, FIGURES
and STATISTICS which help us in decisiondecision
makingmaking. Generally information is the result of
data processing.
For example : PERCENTAGE & GRADE.

HARDWARE
Hardware are the PHYSICAL COMPONENTS
of the Computer System.
Examples :
All the electronic parts.
All cables.
All accessories.

SOFTWARE
SOFTWARE are the logical components of the
computer system. These are basically the
programs and information stored in the
computer.

The hardware and software can be better
explained with the help of a music system.
Hardware :
The device, cassette, tape, wires etc.
Software :
The music stored in the tapes.

Characteristics of Computer
SPEED
STORAGE
ACCURACY
VERSATILITY
AUTOMATION
DILIGENCE

SPEED
The speed with which the computer works can
be understood by the units of measurement of
time within a computer. They are :
MILLI SECOND – 1/1000TH
OF A SECOND
MICRO SECOND – 1/1000TH
OF A MILLI SECOND
NANO SECOND – 1/1000TH
OF A MICRO SECOND
PICO SECOND – 1/1000TH
OF A NANO SECOND

STORAGE
As already discussed a computer can store a
large volume of information.
The factors to be considered for storage are :
•RETREIVAL – IMMEDIATE
•SPACE – VERY LITTLE
•MEDIA – MAGNETIC MEDIA
•LONGIVITY – FOREVER

ACCURACY
The accuracy of the computers is consistently
high. Errors in the machinery may occur, but due
to efficient error-detecting techniques, these very
seldom lead to wrong results. Errors in
computing are due to human rather than
technological weaknesses.
So, we can say that
A COMPUTER NEVER MAKES
ANY MISTAKE

VERSATILITY
Computers seem capable of performing any task, provided
the task can be broken to a series of logical steps.
The computer actually performs only four basic operations :
•Exchanges information with the outside world via INPUT /
OUTPUT devices
•Transfers data within the computer to the different units
•Performs basic arithmetical operations
•Performs operations of comparison
We can reduce the daily activities into steps of the above
operations with the help of ProgrammingProgramming.

AUTOMATION
Once a program to perform a particular
task is stored in the computer, the
individual instructions in the program
are carried out one after the other
automatically to complete the task.
Hence the user requires to just press
certain keys and give the data input. The
data is automatically processed to
produce the output.

DILIGENCE
Being a machine, a computer does not suffer
from the human traits of tiredness and lack of
concentration. If 5 million calculations are to be
performed, it will perform all of them, even the
last one with exactly the same accuracy and
speed.
In fact, there are some computers which are
constantly on for hours, days, months and years
are never switched off.

BASIC STRUCTURE
The computer receives input, processes it and
delivers output.
To perform these tasks it has different units and
each unit is responsible for a specific task.
The units are INPUT, MEMORY, CONTROL
UNIT (CU), ARITHMETIC & LOGIC UNIT
(ALU) AND OUTPUT.
The CU and ALU together are called CENTRAL
PROCESSING UNIT (CPU).

INPUT DEVICEINPUT DEVICE
It is used for transferring data from
the users’ end to the computer.
OUTPUT DEVICEOUTPUT DEVICE
It is used to transfer processed
information from the computer to
the user in a way required by the
user.

MEMORY UNITMEMORY UNIT
It stores instruction and data and provides
them to the various other units as and when
required. It is basically the working memory
of the computer system. This memory unit is
volatile, i.e. it is temporary memory and
nothing can be stored here permanently. The
information is stored in the main memory as
long the computer is switched on or as long
as it is required by the computer.

CONTROL UNITCONTROL UNIT
Controls the various operations
within a computer. It basically
manages all the other units and
devices of the computer system. It
does so by transmitting timing and
control signals to the various devices
and units.

ARITHMETIC & LOGIC UNITARITHMETIC & LOGIC UNIT
It performs the various arithmetic
and logical operations on the data
stored in memory, as dictated by the
instruction.
There are various basic circuits to
perform these operations.

SECONDARY STORAGESECONDARY STORAGE
It stores the various data, information
and programs permanently for future
retrieval. The information is
organised in such a way to retrieve it
in minimum time whenever required.
The stored information remains as
long the user wants it.

BUSBUS
These are a set of connecting wires
used for setting interconnection
between the various devices in the
system. Each set of bus has a specific
function to perform like carrying
data, carrying control signals and
addresses.

BLOCK DIAGRAM
MEMORY
UNIT
INPUT
DEVICE
CONTROL
UNIT
ARITHMETIC
& LOGIC UNIT
OUTPUT
DEVICE
SECONDARY
STORAGE
CONTROL FLOWDATA FLOW
CPU

A character is the smallest amount of
information that can be communicated to
the computer. All data, information and
instruction are represented by a
combination of these characters.
CHARACTER :
DATA REPRESENTATION WITHIN A COMPUTERDATA REPRESENTATION WITHIN A COMPUTER
All alphabets, digits and symbols are
characters. Even a blank space is a
character.

Computer being an electronic device,
can represent only two states –
VOLTAGE and NO VOLTAGE.
Voltage is represented as 1
No voltage is represented as 0
How does the computerHow does the computer
understand a character?understand a character?

A series of such 0s and 1s form a pattern.
1 0 1 1 1 0 0 1
Such a pattern represents a
CHARACTERCHARACTER.
For each character a separate pattern is
there within the computer.

There are eight such positions to represent
0 or 1 and each such position is called a
BIT. Hence the pattern generated to
represent a character is a BIT PATTERN.
01 0 1 1 1 0 1
Two digits, 0 and 1 can generate 256
unique combinations if represented in
eight places. Hence we can represent 256
different characters in any computer.
BIT

ASCII
American Standard Code for
Information Interchange.
It is difficult for us to remember all the 256 bit
patterns and their corresponding characters.
Hence we can convert the bit pattern to a decimal
number. This way each bit pattern will have a
different number and this number, fixed for a
character is called the ASCII code of the
character. All computers follow the same ASCII
code and bit pattern to represent characters.

BINARY
The number system involving two
digits, 0 & 1 is called BINARY.
By using this system a bit pattern
(treated as a binary number) can
be converted to the decimal
number system.

00 0 1 1 1 0 1
32 16 8 1
27
26
25
24
23
22
21
20
= 57
 Starting from right to left, raise 2
to the powerof 0 to 7.
 Add the values corresponding to
the BIT positions having the value
1.

01 0 1 1 1 0 1
128 32 16 8 1
27
26
25
24
23
22
21
20
= 185
0 0 1 0 1 0 1
32 8 1
27
26
25
24
23
22
21
20
0
= 41
11 1 1 1 1 1 1
128 64 32 16 8 4 2 1
27
26
25
24
23
22
21
20
= 255
00 0 0 0 0 0 0
27
26
25
24
23
22
21
20
= 0

BIT
PATTERN
ASCII CODE CHARACTE
R
01000001 65 A
01100001 97 a
00110001 49 1
00101011 43 +
00100000 32
00101101 45 -
00011100 28 (
00101100 44 ,

UNIT FOR MEASUREMENT OFUNIT FOR MEASUREMENT OF
INFORMATIONINFORMATION
8 BIT = 1 CHARACTER = 1 BYTE
1024 BYTES = 1 KILO BYTE (KB)
1024 KB = 1 MEGA BYTE (MB)
1024 MB = 1 GIGA BYTE (GB)
1024 GB = 1 TERA BYTE (TB)

Input devices :Input devices :
KEYBOARDKEYBOARD : It is an input device: It is an input device
to give character based inputs toto give character based inputs to
the computer. All types of data,the computer. All types of data,
instruction and information can beinstruction and information can be
given through the keyboard.given through the keyboard.
HARDWAREHARDWARE

Although the typing portion of theAlthough the typing portion of the
computer keyboard is identical to acomputer keyboard is identical to a
standard typewriter, computers havestandard typewriter, computers have
several additional keys that performseveral additional keys that perform
different functions.different functions.

MOUSEMOUSE : It is used for graphics: It is used for graphics
based inputs. It can mainly selectbased inputs. It can mainly select
some graphical icons and selectsome graphical icons and select
some options from a menu. It cansome options from a menu. It can
not be used for giving data to thenot be used for giving data to the
computer.computer.

SCANNERSCANNER : It is: It is
used forused for
graphical inputs.graphical inputs.
Pictures, images,Pictures, images,
drawings etc. candrawings etc. can
be scanned andbe scanned and
stored in thestored in the
computer.computer.

Operation of the SCANNER :
On the simplest level, a scanner is a device which converts
light (which we see when we look at something) into 0s and
1s (a computer-readable format). In other word, scanners
convert analogue data into digital data.

DIFFERENT INPUT TYPESDIFFERENT INPUT TYPES
MICRMICR : Magnetic Ink Character: Magnetic Ink Character
Recognition.Recognition.
This system uses highly stylizedThis system uses highly stylized
character shapes printed in an inkcharacter shapes printed in an ink
containing magnetic particles.containing magnetic particles.
These characters pre-printed inThese characters pre-printed in
magnetic ink are recognised by amagnetic ink are recognised by a
device called MICR reader.device called MICR reader.
Mainly used in Bank Cheques.Mainly used in Bank Cheques.

MICR CHEQUE
NUMBER

OMROMR : Optical Mark Reading: Optical Mark Reading
Forms and cards are pre-printed forForms and cards are pre-printed for
special purposes so that a mark canspecial purposes so that a mark can
be made in a specified position.be made in a specified position.
Each mark at a position has aEach mark at a position has a
specific meaning and after scanning,specific meaning and after scanning,
the data gets transferred tothe data gets transferred to
computer.computer.
Mainly used in correcting answers toMainly used in correcting answers to
Multiple Choice Question Papers.Multiple Choice Question Papers.

BAR-CODE RECOGNITIONBAR-CODE RECOGNITION : Lines: Lines
or bars can be arranged in a codeor bars can be arranged in a code
and are used particularly forand are used particularly for
labelling goods etc. Bar-codelabelling goods etc. Bar-code
reading is performed by areading is performed by a
scanner. A sequence of bits isscanner. A sequence of bits is
generated and the information isgenerated and the information is
recorded.recorded.

BAR CODE FOR PRODUCT CODE

VOICE INPUTVOICE INPUT : This system: This system
accepts spoken input. Theaccepts spoken input. The
waveform created by the input iswaveform created by the input is
analysed, patterns are extractedanalysed, patterns are extracted
and matched against pre-storedand matched against pre-stored
patterns to identify the input. Thepatterns to identify the input. The
words and phrases the system iswords and phrases the system is
to recognise, are spoken with theto recognise, are spoken with the
system and the patterns aresystem and the patterns are
created for future matching. Forcreated for future matching. For
the voice of more than onethe voice of more than one
person, training with the systemperson, training with the system

OUTPUT DEVICESOUTPUT DEVICES
VDUVDU : Visual Display Unit. Also: Visual Display Unit. Also
called acalled a monitormonitor or aor a screenscreen. It a. It a
device similar to a TV screen. Thedevice similar to a TV screen. The
output on a VDU is temporary.output on a VDU is temporary.

The technology behind monitors and televisions is
The cathode-ray tube, or CRT, A CRT is an sealed
glass bottle with no air inside. It begins with a slim
neck and tapers outward until it forms a large base.
The base is the monitor’s ‘screen’ and is coated on
the inside with a matrix of thousands of tiny
phosphor dots. Phosphors are chemicals which emit
light when excited by a stream of electrons: different
phosphors emit different coloured light.
Each dot consists of three
blobs of coloured phosphor:
one red, one green, one blue.
These groups of three
phosphors make up what is
known as a single pixel.

PRINTERPRINTER : A printer produces: A printer produces
output on paper which can beoutput on paper which can be
permanently kept.permanently kept.
TYPES OF PRINTERS :TYPES OF PRINTERS :
•DOT MATRIXDOT MATRIX
•INK JET PRINTERINK JET PRINTER
•LASER PRINTERLASER PRINTER

Operation of Ink Jet Printer :Operation of Ink Jet Printer :
Inkjet printing, like laser printing, is a non-impactInkjet printing, like laser printing, is a non-impact
method. Ink is emitted from nozzles as they passmethod. Ink is emitted from nozzles as they pass
over a variety of possible media, and the operationover a variety of possible media, and the operation
of an inkjet printer is easy to visualise: liquid ink inof an inkjet printer is easy to visualise: liquid ink in
various colours being squirted at the paper to buildvarious colours being squirted at the paper to build
up an image. A print head scans the page inup an image. A print head scans the page in
horizontal strips, using a motor assembly to move ithorizontal strips, using a motor assembly to move it
from left to right and back, as another motorfrom left to right and back, as another motor
assembly rolls the paper in vertical steps. A strip ofassembly rolls the paper in vertical steps. A strip of
the image is printed, then the paper moves on, readythe image is printed, then the paper moves on, ready
for the next strip. To speed things up, the print headfor the next strip. To speed things up, the print head
doesn’t print just a single row of pixels in each pass,doesn’t print just a single row of pixels in each pass,
but a vertical row of pixels at a time.but a vertical row of pixels at a time.

Most inkjets use thermal technology, whereby heatMost inkjets use thermal technology, whereby heat
is used to fire ink onto the paper. There are threeis used to fire ink onto the paper. There are three
main stages with this method. The squirt is initiatedmain stages with this method. The squirt is initiated
by heating the ink to create a bubble until theby heating the ink to create a bubble until the
pressure forces it to burst and hit the paper. Thepressure forces it to burst and hit the paper. The
bubble then collapses as the element cools, and thebubble then collapses as the element cools, and the
resulting vacuum draws ink from the reservoir toresulting vacuum draws ink from the reservoir to
replace the ink that was ejected.replace the ink that was ejected.

Operation of a LASER printer :
Where the image to be printed is communicated to it via a
page description language, the printer’s first job is to convert
the instructions into a bitmap. This is done by the printer’s
internal processor, and the result is an image (in memory) of
which every dot will be placed on the paper.
At the heart of the laser printer is a small rotating drum - the
organic photo-conducting cartridge (OPC) - with a coating
that allows it to hold an electrostatic charge. A laser beam
scans across the surface of the drum, selectively imparting
points of positive charge onto the drum's surface that will
ultimately represent the output image. The area of the drum is
the same as that of the paper onto which the image will
eventually appear, every point on the drum corresponding to
a point on the sheet of paper. In the meantime, the paper is
passed through an electrically charged wire which deposits a
negative charge onto it.

DOT MATRIX INK-JET
LASER

DOTDOT
MATRIXMATRIX
INKINK
JETJET
LASERLASER
CHARACTECHARACTE
R BASEDR BASED
OUTPUTOUTPUT
YESYES YESYES YESYES
GRAPHICSGRAPHICS
BASEDBASED
OUTPUTOUTPUT
NONO GOODGOOD EXCELLENEXCELLEN
TT
OUTPUTOUTPUT
QUALITYQUALITY
OKOK GOODGOOD EXCELLENEXCELLEN
TT
COSTCOST
EFFECTIVEEFFECTIVE
LOWLOW
RECURRINRECURRIN
G COSTG COST
HIGHHIGH
RECURRINRECURRIN
G COSTG COST
VERY HIGHVERY HIGH
RECURRINRECURRIN
G COSTG COST
COLORCOLOR NONO OKOK EXCELLENEXCELLEN
TT

PLOTTERPLOTTER : It is a special kind of: It is a special kind of
printer for printing drawings onprinter for printing drawings on
large sheets of paper.large sheets of paper.

STORAGE DEVICESSTORAGE DEVICES
HARD DISK :HARD DISK : It a device fixed to aIt a device fixed to a
computer and can store largecomputer and can store large
volumes of information. It usesvolumes of information. It uses
magnetic media and electromagnetic media and electro
magnetic theory to read and storemagnetic theory to read and store
information.information.
The standard capacity : 10 – 20The standard capacity : 10 – 20
GBGB

FLOPPY DISK :FLOPPY DISK : It is a cassette likeIt is a cassette like
device to store information. It isdevice to store information. It is
external to a computer and can be putexternal to a computer and can be put
into a floppy disk drive (FDD) attachedinto a floppy disk drive (FDD) attached
to a computer for reading and writingto a computer for reading and writing
information. It also uses electroinformation. It also uses electro
magnetic theory.magnetic theory.
Since it is not fixed to a computer,Since it is not fixed to a computer,
information can be copied from theinformation can be copied from the
hard disk of a computer to a floppy andhard disk of a computer to a floppy and
can be used in another computer.can be used in another computer.
Standard capacity : 1.44 MBStandard capacity : 1.44 MB

CD :CD : It stands for COMPACT DISK. ItIt stands for COMPACT DISK. It
is the same as any other music oris the same as any other music or
video CD. It is also external to avideo CD. It is also external to a
computer and can be put into a CDcomputer and can be put into a CD
drive attached to a computer fordrive attached to a computer for
reading information. It uses OPTICALreading information. It uses OPTICAL
technology to read information.technology to read information.
Information once written into a CD canInformation once written into a CD can
not be erased or changed. Hence it isnot be erased or changed. Hence it is
called a ROM (Read Only Memory).called a ROM (Read Only Memory).
Standard capacity : 650 MBStandard capacity : 650 MB

FLOPPY
DISK
HARD DISK
CD ROM

Hard drives are magnetic storage devices that
contain several discs inside called "Platters" that
are attached to a spindle motor. The number of
platters varies depending on the capacity of the
drive. Platters are coated with a film of
magnetically sensitive substance that is primarily
made of iron oxide. Another important ingredient is
a thin layer of cobalt alloy.
The read/write heads are
responsible for reading and
writing to the platters and
are attached to the head
actuator which is in charge
of moving the heads around
the platters.

There’s a read/write head for each
side of each platter, mounted on
arms which can move them
towards the central spindle or
towards the edge. The arms are
moved by the head actuator, which
contains a voice-coil - an
electromagnetic coil that can move
a magnet very rapidly. Loudspeaker
cones are vibrated using a similar
mechanism.
The heads are designed to touch the platters when the
disk stops spinning - that is, when the drive is powered
off. During the spin-down period, the airflow diminishes
until it stops completely, when the head lands gently on
the platter surface - to a dedicated spot called the landing
zone (LZ). The LZ is dedicated to providing a parking spot
for the read/write heads, and never contains data.

When a disk undergoes a low-level format, it is divided it into
tracks and sectors. The tracks are concentric circles around
the central spindle on either side of each platter. Tracks
physically above each other on the platters are grouped
together into cylinders which are then further subdivided into
sectors of 512 bytes apiece. The sector is a disk's smallest
accessible unit. To improve performance, data sectors are
allocated in groups called clusters.

Floppy drives are the slots on the front
of your computer that you insert disks
into, copy files to, and install programs
from. These drives accept 3½" disks.
These diskettes come in different
densities. The standard disks of today
are called high-density. They usually
hold 1.44 MB of data. The newest disks
are called extended-capacity and they
hold 2.88 MB.

Floppy disks are also a form of
magnetic storage that function
similarly to hard drives. There is a
spring loaded metal cover that is
moved aside during operation that
exposes a mylar disk that is coated
with a ferro-magnetic substance.
The drive's read/write heads access
the disk as it turns on a spindle.

The Compact Disc itself is a thinThe Compact Disc itself is a thin
plastic disk some 12 cm. in diameter.plastic disk some 12 cm. in diameter.
Information is encoded in a plastic-Information is encoded in a plastic-
encased spiral track contained onencased spiral track contained on
the top of the disk.the top of the disk.
The spiral track is read optically by aThe spiral track is read optically by a
noncontact head which scansnoncontact head which scans
approximately radially as the diskapproximately radially as the disk
spins just above it.spins just above it.

MEMORYMEMORY : There are two types of: There are two types of
memory : RAM & ROM.memory : RAM & ROM.
RAMRAM : Random Access Memory. It: Random Access Memory. It
is the main memory of theis the main memory of the
computer. It is volatile memorycomputer. It is volatile memory
and the information gets erasedand the information gets erased
whenever the power supply iswhenever the power supply is
switched off.switched off.

There are different types of RAM:
Static RAM (SRAM)Static RAM (SRAM) This RAM will maintain its
data as long as power is provided to the memory
chips. It does not need to be rewritten periodically.
SRAM is very fast but much more expensive than
DRAM. SRAM is often used as cache memory due to
its speed. (CACHE memory is the memory used
directly by the CPU).
Dynamic RAM (DRAM)Dynamic RAM (DRAM) DRAM, unlike SRAM,
must be continually rewritten in order for it to
maintain its data. This is done by placing the
memory on a refresh circuit that rewrites the data
several hundred times per second. DRAM is used for
most system memory because it is cheap and small.

ROMROM : Read Only Memory: Read Only Memory
Information is burnt into the ROMInformation is burnt into the ROM
chip at the time of manufacturing.chip at the time of manufacturing.
It can not be erased or altered andIt can not be erased or altered and
fresh information can not befresh information can not be
written into the ROM. The BIOS iswritten into the ROM. The BIOS is
stored on ROM because the userstored on ROM because the user
cannot disrupt the information.cannot disrupt the information.
BIOS : Basic Input Output System.
It contains some instructionsIt contains some instructions
required internally by therequired internally by the
computer.computer.

There are different types of ROM.
Programmable ROM (PROM)Programmable ROM (PROM) This is basically a blank
ROM chip that can be written to once. It is much like a CD-R
drive that burns the data into the CD. Some companies use
special machinery to write PROMs for special purposes.
Erasable Programmable ROM (EPROM)Erasable Programmable ROM (EPROM) This is just like
PROM except that you can erase the ROM by shining a special
ultra-violet light into a sensor atop the ROM chip for a certain
amount of time. Doing this wipes the data out, allowing it to
be rewritten.
Electrically Erasable Programmable ROM (EEPROM)Electrically Erasable Programmable ROM (EEPROM)
(Also called Flash BIOS) This ROM can be rewritten through
the use of a special software program. Flash BIOS also
operates this way, allowing users to upgrade their BIOS.
ROM is slower than RAM, which is why some try to shadow it
to increase speed.

CPU :CPU : Central Processing Unit. ItCentral Processing Unit. It
is also called the micro processor.is also called the micro processor.
There are CPUs with varyingThere are CPUs with varying
efficiency and the quality of theefficiency and the quality of the
computer depends mainly on thecomputer depends mainly on the
CPU present on the main board.CPU present on the main board.

Example of some CPUs by Intel.Example of some CPUs by Intel.
•80888088 19851985
•8038680386 19871987
•8048680486 19881988
•Pentium – IPentium – I 19901990
•Pentium – IIPentium – II 19941994
•Pentium - IIIPentium - III 19951995
•Pentium – IVPentium – IV 20012001

MOTHER BOARD :MOTHER BOARD : The mainThe main
circuit board housing thecircuit board housing the
microprocessor, RAM, ROM andmicroprocessor, RAM, ROM and
connecting interfaces to theconnecting interfaces to the
various other devices andvarious other devices and
peripherals.peripherals.

CABINET HOLDING THE MOTHERCABINET HOLDING THE MOTHER
BOARD AND OTHER COMPONENTSBOARD AND OTHER COMPONENTS

A DESKTOP PERSONALA DESKTOP PERSONAL
COMPUTERCOMPUTER

SOFTWARE :SOFTWARE :
A set of programs that utilises theA set of programs that utilises the
hardware and uses its’ capabilitieshardware and uses its’ capabilities
to perform various tasks.to perform various tasks.
ProgramProgram : A program is a set of: A program is a set of
instructions stored in the computerinstructions stored in the computer
to solve specific problems.to solve specific problems.

C L A S S IF IC A T IO N O F S O F T W A R E
O P E R A T IN G S Y S T E M
IN T E R P R E T E R C O M P IL E R
T R A N S L A T O R S
S Y S T E M
R E A D Y -M A D E C U S T O M IS E D
A P P L IC A T IO N
S O F T W A R E

SYSTEM SOFTWARE : TheSYSTEM SOFTWARE : The
system s/w are a set of programssystem s/w are a set of programs
specially designed for performingspecially designed for performing
tasks such as, controlling thetasks such as, controlling the
computer hardware, and utilisingcomputer hardware, and utilising
the resources to help thethe resources to help the
application software solve specificapplication software solve specific
problems.problems.

OPERATING SYSTEM : ProgramsOPERATING SYSTEM : Programs
to control the hardware andto control the hardware and
provide user interface. It isprovide user interface. It is
essential for every computer.essential for every computer.
Functions :Functions :
•Memory managementMemory management
•CPU managementCPU management
•Input / Output managementInput / Output management
•Storage / File managementStorage / File management
•Provide user interfaceProvide user interface

TRANSLATORTRANSLATOR : Translates high: Translates high
level language to low levellevel language to low level
language and vice-versa.language and vice-versa.
LOW LEVEL LANGUAGELOW LEVEL LANGUAGE : The: The
language of bits understoodlanguage of bits understood
directly by the computer. It is alsodirectly by the computer. It is also
called the machine language.called the machine language.
HIGH LEVEL LANGUAGEHIGH LEVEL LANGUAGE : The: The
language of users understood bylanguage of users understood by
the computer only afterthe computer only after

A computer language comprisesA computer language comprises
of key words and syntax. Usingof key words and syntax. Using
the key words and following thethe key words and following the
syntax, commands andsyntax, commands and
instructions are written step byinstructions are written step by
step to develop the program.step to develop the program.
The program is then translatedThe program is then translated
into machine language by usinginto machine language by using
the translators.the translators.

There are many languages andThere are many languages and
any one can be used to developany one can be used to develop
programs.programs.
Each language has it’s capabilitiesEach language has it’s capabilities
and limitations.and limitations.
COBOL Commercial applications
BASIC Beginners’ language
FORTRA
N
Mathematical and scientific
applications
C System level programming

There are two types ofThere are two types of
translators :translators :
INTERPRETER & COMPILER.INTERPRETER & COMPILER.
An interpreter takes oneAn interpreter takes one
instruction at a time, translates itinstruction at a time, translates it
and moves on to the nextand moves on to the next
statement in the program. Hence,statement in the program. Hence,
executing the entire program stepexecuting the entire program step
by step.by step.
Each time we execute a programEach time we execute a program
the source program and thethe source program and the
interpreter, both are required.

A compiler takes all the high levelA compiler takes all the high level
language instructions at a timelanguage instructions at a time
and creates a correspondingand creates a corresponding
machine language program whichmachine language program which
can be directly executed by thecan be directly executed by the
computer. Hence, aftercomputer. Hence, after
compilation neither the sourcecompilation neither the source
program nor the compiler programprogram nor the compiler program
is required.is required.HIGH
LEVEL
LANGUAG
E
PROGRA
M
MACHINE
LANGUAG
E
PROGRA
M
TRANSLATION &
COMPILATION

APPLICATION SOFTWARE :APPLICATION SOFTWARE :
These are programs developedThese are programs developed
using one of the languages tousing one of the languages to
perform a specific task.perform a specific task.

READY MADE :READY MADE :
These are programs developed byThese are programs developed by
software companies for generalsoftware companies for general
purpose applications. Thesepurpose applications. These
programs can be bought and canprograms can be bought and can
be installed in the hard disk of abe installed in the hard disk of a
computer.computer.
Examples : MS-WORD, FACT,Examples : MS-WORD, FACT,
TALLY, FOXPRO etc.TALLY, FOXPRO etc.

CUSTOMISED OR TAILORCUSTOMISED OR TAILOR
MADE :MADE :
These are programs developed forThese are programs developed for
SPECIFIC USER REQUIREMENTSPECIFIC USER REQUIREMENT
within an organisation. Thesewithin an organisation. These
programs are developed byprograms are developed by
programmers as per the userprogrammers as per the user
requirements.requirements.
Examples : Mark-sheet, Salary,Examples : Mark-sheet, Salary,
Sales information, RailwaySales information, Railway
reservation etc.reservation etc.

MS-DOSMS-DOS
MicrosoftMicrosoft
Disk Operating SystemDisk Operating System

FILE :FILE :
Related information or data isRelated information or data is
stored in the form of a file in thestored in the form of a file in the
disk. Hence, the minimum chunkdisk. Hence, the minimum chunk
of information that we can storeof information that we can store
in or retrieve form a disk, is ain or retrieve form a disk, is a
file.file.
The files are either program filesThe files are either program files
or data files.or data files.

Each file must have a uniqueEach file must have a unique
name.name.
The file name has two parts :The file name has two parts :
PRIMARY NAMEPRIMARY NAME &&
SECONDARY NAMESECONDARY NAME oror
extension.extension.
The primary name is to identifyThe primary name is to identify
the contents and the extensionthe contents and the extension
is to identify the type of the file.is to identify the type of the file.

The primary file name can beThe primary file name can be
maximum 8 characters long.maximum 8 characters long.
The extension of the file nameThe extension of the file name
can be maximum 3 characterscan be maximum 3 characters
long.long.
The primary file name and theThe primary file name and the
extension is joined by a period.extension is joined by a period.
The extension is optional.The extension is optional.

Legal characters in the file namesLegal characters in the file names
include all letters of the alphabet,include all letters of the alphabet,
numeric digits and punctuationnumeric digits and punctuation
marksmarks except the following
characters ::
* ? = + | : [ ] ; , / < > “* ? = + | : [ ] ; , / < > “
A blank spaceA blank space can notcan not be used inbe used in
the file name.the file name.
Capital & small letters are treatedCapital & small letters are treated
as the same.as the same.

BIODATA.TX
T
SALARY.98
ACCOUNTS
.COM
1
A.B
MY
FILE.DOC
VALID
VALID
VALID
INVALID
VALID
VALID
INVALID

WILD CARD :WILD CARD :
The wild card allows us to deal withThe wild card allows us to deal with
more than one file at a time and helpsmore than one file at a time and helps
us to group the files.us to group the files.
** A substitute at the beginningA substitute at the beginning
? A substitute at specific positions? A substitute at specific positions

*.TXT
Primary name – anything
Extension - .TXT
BIODATA.TXT
BOOK.TXT
NOTES.TXT
SALARY.*
Primary name – SALARY
Extension - anything
SALARY.98
SALARY.DAT
SALARY.DOC
A*.*
Primary name – starting with A
ALASKA.DOC
ABC.123
A
*.*
All files
*.
Extension – nothing (must not be there)
SALARY
BIODATA

?A*.TXT
Primary name – second character A
Extension - .TXT
SALARY.TXT
DATA.TXT
RANA.TXT
*.?O?
Extension – second character O
SALARY.DOC
COMMAND.COM
NOTES.SOS

DRIVE NAMESDRIVE NAMES
A computer can have more than oneA computer can have more than one
disk drives like hard disk, floppy diskdisk drives like hard disk, floppy disk
drive & CD-rom drive.drive & CD-rom drive.
Each of these drives are identified byEach of these drives are identified by
an alphabet and a colon symbol asan alphabet and a colon symbol as
A:, B:, C: etc.A:, B:, C: etc.

FIRST FLOPPY DISK DRIVE : A:
SECOND FLOPPY DISK DRIVE : B:
FIRST HARD DISK : C:
Rest of the drives are named as D: onwards.
CD-ROM DRIVE: D:
If the computer has a second hard disk and a
cd-rom drive –
SECOND HARD DISK: D:
CD-ROM DRIVE : E:

In order to make the computer
work, the operating system
program files must be loaded into
the memory from the disk. This
process is automatically initiated
as soon as a computer is
switched on. This process is
called bootingbooting..
The booting takes place with theThe booting takes place with the
help of instructions in the ROM.help of instructions in the ROM.

Following tasks are carried out during
booting :
• Test the computer hardware
•Check all the devices
•Load the operating system files from
the disk
The computer is ready to interact with
the user only after booting is carried
out successfully.

DOS program files necessaryDOS program files necessary
for booting :for booting :
IO.SYSIO.SYS
Responsible for the INPUT / OUTPUT operations
MSDOS.SYSMSDOS.SYS
Responsible for the DISK & FILE operations
COMMAND.COMCOMMAND.COM
Acts as the command interpreter to translate the user instructions.

After booting the command line prompt
appears on the screen. Any dos command
statement is typed at the command prompt
and an <enter> key is pressed to execute
it.
C:>=
Current
drive
Cursor
Cursor indicates the point on the screen at which the next
character or the output will be displayed.

DEFAULT DRIVEDEFAULT DRIVE : This is the current drive in
which DOS will look for the files and carry out all
the operations in this drive until we specify
otherwise.
C:>C:>== ((DOS prompt where current default drive is
C:)
We can change the default drive just by typing
the drive name at the prompt.
C:>C:> A:A: <ENTER><ENTER>
A:>A:>== ((DOS prompt where current default drive is A:)

OME ELEMENTARY DOS COMMANDSOME ELEMENTARY DOS COMMANDS
CLSCLS
This command clears the screenThis command clears the screen
and takes the prompt to the left-topand takes the prompt to the left-top
corner of the screen.corner of the screen.

DATEDATE
To change the system date.To change the system date.
On typing this command the currentOn typing this command the current
date is displayed and the user isdate is displayed and the user is
allowed to type in the new date.allowed to type in the new date.

TIMETIME
To change the system time.To change the system time.
On typing this command the currentOn typing this command the current
time is displayed and the user istime is displayed and the user is
allowed to type in the new time.allowed to type in the new time.

DIRDIR
This command gives a listing, calledThis command gives a listing, called
the directory, of the files stored on athe directory, of the files stored on a
disk.disk.
It displays :It displays :
•file namesfile names
•SizeSize
•date & time when the file was created or updated.date & time when the file was created or updated.

Options with DIROptions with DIR
DIR /PDIR /P Pause after every screen full of information.Pause after every screen full of information.
DIR /WDIR /W Wide format displaying only the file names.Wide format displaying only the file names.
DIR /ONDIR /ON In order of file name.In order of file name.
DIR /OEDIR /OE In order of extension.In order of extension.
DIR /OSDIR /OS In order of size.In order of size.
DIR /ODDIR /OD In order of date.In order of date.

Wild cards can be used with DIR toWild cards can be used with DIR to
display a group of files satisfying thedisplay a group of files satisfying the
wild card criteria.wild card criteria.
DIR *.TXTDIR *.TXT Files with extension .TXTFiles with extension .TXT
DIR SALARY.*DIR SALARY.* Files with name SALARYFiles with name SALARY

The directory of another drive can beThe directory of another drive can be
displayed by specifying the drivedisplayed by specifying the drive
name with the command.name with the command.
DIR A:DIR A: Displays the directory of the floppy in driveDisplays the directory of the floppy in drive
A.A.

BASIC FILE COMMANDSBASIC FILE COMMANDS
COPYCOPY Make copies of files.Make copies of files.
SYNTAXSYNTAX
COPY [SOURCE] [TARGET]COPY [SOURCE] [TARGET]
The source has to be a file name or wildcardThe source has to be a file name or wildcard
specification. It may or may not have a drive name. It itspecification. It may or may not have a drive name. It it
does not have a drive name, the file(s) is collected fromdoes not have a drive name, the file(s) is collected from
the default drive.the default drive.
The target may be a file name or a drive name.The target may be a file name or a drive name.

Copy from one disk to another :Copy from one disk to another :
C:>COPY MYFILE.TXT A:C:>COPY MYFILE.TXT A:
Copies the file from the default drive ( C: ) to A:Copies the file from the default drive ( C: ) to A:
C:>COPY *.TXT A:C:>COPY *.TXT A:
Copies the files with extension .TXT from the defaultCopies the files with extension .TXT from the default
drive ( C: ) to A:drive ( C: ) to A:

C:>COPY A:SALARY.DATC:>COPY A:SALARY.DAT
Copies the file from A: to the default drive ( C: )Copies the file from A: to the default drive ( C: )
In this case, since the target is the default drive it mayIn this case, since the target is the default drive it may
not be written in the command.not be written in the command.
C:>COPY A:*.* B:*.*C:>COPY A:*.* B:*.*
Copies all files the first floppy drive to the secondCopies all files the first floppy drive to the second
floppy drive.floppy drive.
In this case, the current or the default drive is not at allIn this case, the current or the default drive is not at all
involved in the copying.involved in the copying.

While making a copy of a file we canWhile making a copy of a file we can
also change the name of the file.also change the name of the file.
C:>C:>COPY MYFILE.TXTCOPY MYFILE.TXT
A:YOURFILE.TXTA:YOURFILE.TXT
Copies the file from the default drive ( C: ) to A: andCopies the file from the default drive ( C: ) to A: and
the name of the file in drive A: changes.the name of the file in drive A: changes.

We can make copies of the files inWe can make copies of the files in
the same disk also. But, whilethe same disk also. But, while
copying in the same disk, the namecopying in the same disk, the name
of the target file must be specified asof the target file must be specified as
different than the source file.different than the source file.
C:>C:>COPY STUDENT.DOCCOPY STUDENT.DOC
PUPIL.DOCPUPIL.DOC
C:>C:>COPY *.TXT *.DOCCOPY *.TXT *.DOC

COMBINE THE CONTENTS OFCOMBINE THE CONTENTS OF
SEVERAL FILES INTO ONE FILE :SEVERAL FILES INTO ONE FILE :
COPY POEM1.TXT+POEM2.TXT POEM3.TXTCOPY POEM1.TXT+POEM2.TXT POEM3.TXT
This will combine the contents of theThis will combine the contents of the
files POEM1.TXT & POEM2.TXT andfiles POEM1.TXT & POEM2.TXT and
create a new file namedcreate a new file named
POEM3.TXT.POEM3.TXT.

DELETING FILES:DELETING FILES:
Files can be removed one at a time orFiles can be removed one at a time or
several files at a time by using wildseveral files at a time by using wild
cards. The commands are DEL or ERASE.cards. The commands are DEL or ERASE.
DEL BIODATA.DOCDEL BIODATA.DOC Deletes the fileDeletes the file
BIODATA.DOC.BIODATA.DOC.
DEL *.txtDEL *.txt Deletes all files having extension .TXTDeletes all files having extension .TXT
DEL *.*DEL *.* Deletes all the files.Deletes all the files.
The command ERASE can also be usedThe command ERASE can also be used
the same way in place of DEL.the same way in place of DEL.

RENAME FILES:RENAME FILES:
SYNTAX :SYNTAX :
REN OLD-NAME NEW-NAMEREN OLD-NAME NEW-NAME
REN STUDENT.99 STUDENT.00REN STUDENT.99 STUDENT.00
The name of the file STUDENT.99 changes toThe name of the file STUDENT.99 changes to
STUDENT.00STUDENT.00
REN *.99 *.00REN *.99 *.00
The extension of all .99 files change to .00The extension of all .99 files change to .00

DIPLAYING FILE CONTENTS :DIPLAYING FILE CONTENTS :
TYPE BIODATA.TXTTYPE BIODATA.TXT
This will display the contents of the file BIODATA.TXTThis will display the contents of the file BIODATA.TXT
Wild card can not be used with thisWild card can not be used with this
command, hence only one file can becommand, hence only one file can be
displayed at a time using the TYPEdisplayed at a time using the TYPE
COMMAND.COMMAND.
TYPE displays the contents of text filesTYPE displays the contents of text files
only.only.

CREATE A SMALL TEXT FILE USINGCREATE A SMALL TEXT FILE USING
COPY :COPY :
COPY CON NEWFILE.TXTCOPY CON NEWFILE.TXT
The cursor comes to the next line and we can enterThe cursor comes to the next line and we can enter
the text line after line. On completion of typing usethe text line after line. On completion of typing use
ctrl+Z to store the file.ctrl+Z to store the file.

A sub-directory is a separate storageA sub-directory is a separate storage
location in the disk where files can belocation in the disk where files can be
stored. This helps us to organise the filesstored. This helps us to organise the files
in separate locations in the disk.in separate locations in the disk.
There can be several subdirectories in aThere can be several subdirectories in a
disk and the subdirectories are named thedisk and the subdirectories are named the
same way as the files.same way as the files.
SUB-DIRECTORY :SUB-DIRECTORY :

The first directory that is always there in a disk is calledThe first directory that is always there in a disk is called
thethe rootroot directory. All other directories are createddirectory. All other directories are created
under the root directory in different levels.under the root directory in different levels.
LETTER
ROOT
STUDENT ACCOUNT TEXT OTHER
MARKS

PATH or ADDRESS of a directory or sub-directory :PATH or ADDRESS of a directory or sub-directory :
The path helps us to access a directory. It always startsThe path helps us to access a directory. It always starts
from the root and ends with the destination directory.from the root and ends with the destination directory.
LETTER
ROOT
MARKS

STUDENTMARKS TEXTLETTER

ROOT
MARKS LETTER
CREATING SUB-DIRECTORIES
Command : MD or MKDIR
MD STUDENT
MD ACCOUNT
MD TEXT
MD OTHER
MD STUDENTMARKS
MD TEXTLETTER

C:>CD STUDENT
C:STUDENT>=
ACCOUNT
ROOT
STUDENT TEXT OTHER
MARKS LETTER
CHANGING FROM ONE
DIRECTORY TO ANOTHER
Command : CD
C:STUDENT>CD MARKS
C:STUDENTMARKS>=
C:STUDENTMARKS>CD OTHER
C:OTHER>=
C:OTHER>CD
C:>=

COPYING FILES :
C:>COPY STUDENTNOTES.TXT TEXT
Copies the file NOTES.TXT from the sub-directory STUDENT to TEXT
C:>COPY STUDENTNOTES.TXT TEXT
SUB-
DIRECTORIES
FILE

MORE EXAMPLES :
C:>COPY OTHER*.* ACCOUNT
Copies all the files from the sub-directory OTHER to ACCOUNT
C:>COPY OTHER*.*
Copies all the files from the sub-directory OTHER to root directory
C:>COPY *.DOC STUDENTMARKS
Copies all the files from the root directory to the sub-directory MARKS
C:>COPY TEXTLETTER*.* A:
Copies all files from the sub-directory LETTER to the drive A

ROOT
MARKS LETTER
REMOVING SUB-DIRECTORIES
Command : RD or RMDIR
DEL STUDENTMARKS*.*
RD STUDENTMARKS
We can not remove a sub-directory:
•If it is not empty
•Staying in the same sub-directory
DEL STUDENT*.*
RD STUDENT

INTERNAL & EXTERNAL COMMANDS
Internal commandsInternal commands are loaded at the time of
booting and are always available in the
memory. Hence these commands can be
executed any time after booting.
Example: DIR, COPY, TYPE, CD, MD, RD etc.
In fact all the commands we have discussed till
now are Internal Commands.

External commandsExternal commands are separate utility
programs that accompany the operating system.
These commands are executed with the help of
program files present in the disk. Typically the
primary name of a program file for a particular
external command is the same as the command
itself and the extension is either .COM or .EXE.
Example: TREE, FORMAT, LABEL, SYS,
DISKCOPY, ATTRIB, SCANDISK, MORE etc.

TREETREE - To display the sub-directory structure of a disk.
C:> TREE C:
Displays the sub-directory structure starting from
root directory.
C:> TREE C:TEXT
Displays the sub-directory structure starting from
the sub-directory TEXT.
C:> TREE C: /F
The option F includes the files also in each sub-
directory.

FORMAT – Prepares a blank disk for receiving
and storing data or creates a new blank disk from
a used one. Formatting an used disk will erase all
the contents and make it a new blank disk.
C:> FORMAT A:
Formats the floppy disk in A: drive
C:> FORMAT A: /S
The option S makes the disk bootable after
formatting.
DO NOT format the HARD DISK or all
the contents will be lost.

LABEL – Adds or modifies the volume label of
the disk.
C:> LABEL C:
Allows you to change the volume label of the Hard
disk.

SYS – Copies the DOS system files into a disk and
makes it bootable.
C:> SYS A:
Will transfer the system files to the floppy in drive
A: and make it bootable.

DISKCOPY – Copies an entire disk into
another and makes an identical disk. It overwrites
the contents of the target disk.
C:> DISKCOPY A: B:
Will copy the contents of the floppy in drive A: to
the floppy in drive B:

ATTRIB – Changes the attributes of a file. A file
can be made read-only or hidden.
C:> ATTRIB +R MYFILE.TXT
Makes the file read-only.
C:> ATTRIB +H MYFILE.TXT
Makes the file hidden.
C:> ATTRIB -R –H MYFILE.TXT
Removes the read-only and hidden attributes.
Wild cards can be used to change the
attributes of a group of files.

SCANDISK – Analyses and repairs logical and
physical disk errors.
It identifies the bad sectors from the disk
and marks them so that no data is stored
there.
C:> SCANDISK C:

MORE – Displays the output one screen at a
time instead of continuous scrolling.
This command does not have any
function alone and is always used in
association with another command
which displays some output. PIPING
SIGN is given between the command and
more.
C:> TREE C:/ | MORE
Displays the subdirectory structure page-wise.

End of show.End of show.
Thank you.Thank you.

Introduction to computers

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