Introduction to computers

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


Study Note developed by

S. Agarwal, Lecturer & Systems Incharge, ,

St. Xavier’s Computer St. Xavier’s Computer CentreCentre

St. Xavier’s CollegeSt. Xavier’s College

KolkataKolkataJuly-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 decision decision makingmaking. Generally information is the result of data processing.

For example : PERCENTAGE & GRADE.


HARDWAREHardware 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

SPEEDSTORAGE

ACCURACYVERSATILITYAUTOMATION

DILIGENCE


SPEEDThe 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


STORAGEAs 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 – FOR EVER


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


VERSATILITYComputers 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.


AUTOMATIONOnce 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.


DILIGENCEBeing 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 STRUCTUREThe 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 UNITIt 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

CONTROLUNIT

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 computer How 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 1Such 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 power of 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 0 027 26 25 24 23 22 21 20

= 0


BIT PATTERN

ASCII CODE CHARACTER

01000001

65 A

01100001

97 a

00110001

49 1

00101011

43 +

00100000

32

00101101

45 -

00011100

28 (

00101100

44 ,



UNIT FOR MEASUREMENT OF UNIT 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 : It is an input device to give character based device to give character based inputs to the computer. All inputs to the computer. All types of data, instruction and types of data, instruction and information can be given information can be given through the keyboard.through the keyboard.

HARDWAREHARDWARE


Although the typing portion of the Although the typing portion of the computer keyboard is identical to a computer keyboard is identical to a standard typewriter, computers have standard typewriter, computers have several additional keys that perform several additional keys that perform

different functions.different functions.


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



SCANNERSCANNER : It is : It is used for used for graphical graphical inputs. inputs.

Pictures, Pictures, images, images, drawings etc. drawings etc. can be scanned can be scanned and stored in and stored in the computer.the 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 stylized This system uses highly stylized character shapes printed in an character shapes printed in an ink containing magnetic ink containing magnetic particles. These characters pre-particles. These characters pre-printed in magnetic ink are printed in magnetic ink are recognised by a device called recognised by a device called MICR reader.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 Forms and cards are pre-printed for special purposes so that a for special purposes so that a mark can be made in a specified mark can be made in a specified position. Each mark at a position position. Each mark at a position has a specific meaning and after has a specific meaning and after scanning, the data gets scanning, the data gets transferred to computer.transferred to computer.

Mainly used in correcting answers Mainly used in correcting answers to Multiple Choice Question to Multiple Choice Question Papers.Papers.




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


BAR CODE FOR PRODUCT CODE


VOICE INPUTVOICE INPUT : This system : This system accepts spoken input. The accepts spoken input. The waveform created by the input waveform created by the input is analysed, patterns are is analysed, patterns are extracted and matched against extracted and matched against pre-stored patterns to identify pre-stored patterns to identify the input. The words and the input. The words and phrases the system is to phrases the system is to recognise, are spoken with the recognise, are spoken with the system and the patterns are system and the patterns are created for future matching. created for future matching. For the voice of more than one For the voice of more than one person, training with the person, training with the system must be done system must be done separately.separately.


OUTPUT DEVICESOUTPUT DEVICES

VDUVDU : Visual Display Unit. Also : Visual Display Unit. Also called a called a monitormonitor or a or a screenscreen. It . It a device similar to a TV screen. a device similar to a TV screen. The output on a VDU is The output on a VDU is temporary.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 be output 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-impact Inkjet printing, like laser printing, is a non-impact method. Ink is emitted from nozzles as they pass method. Ink is emitted from nozzles as they pass over a variety of possible media, and the operation over a variety of possible media, and the operation of an inkjet printer is easy to visualise: liquid ink in of an inkjet printer is easy to visualise: liquid ink in various colours being squirted at the paper to build various colours being squirted at the paper to build up an image. A print head scans the page in up an image. A print head scans the page in horizontal strips, using a motor assembly to move it horizontal strips, using a motor assembly to move it from left to right and back, as another motor from left to right and back, as another motor assembly rolls the paper in vertical steps. A strip of assembly rolls the paper in vertical steps. A strip of the image is printed, then the paper moves on, ready the image is printed, then the paper moves on, ready for the next strip. To speed things up, the print head for 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 heat Most inkjets use thermal technology, whereby heat is used to fire ink onto the paper. There are three is used to fire ink onto the paper. There are three main stages with this method. The squirt is initiated main stages with this method. The squirt is initiated by heating the ink to create a bubble until the by heating the ink to create a bubble until the pressure forces it to burst and hit the paper. The pressure forces it to burst and hit the paper. The bubble then collapses as the element cools, and the bubble then collapses as the element cools, and the resulting vacuum draws ink from the reservoir to resulting 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


DOT DOT

MATRIXMATRIXINKINK

JETJETLASERLASER

CHARACTER CHARACTER BASED BASED OUTPUTOUTPUT

YESYES YESYES YESYES

GRAPHICS GRAPHICS BASED BASED OUTPUTOUTPUT

NONO GOODGOOD EXCELLENTEXCELLENT

OUTPUTOUTPUT

QUALITYQUALITYOKOK GOODGOOD EXCELLENTEXCELLENT

COST COST EFFECTIVEEFFECTIVE

LOW LOW RECURRINRECURRING COSTG COST

HIGH HIGH RECURRINRECURRING COSTG COST

VERY HIGH VERY HIGH RECURRINRECURRING COSTG COST

COLORCOLOR NONO OKOK EXCELLENTEXCELLENT


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


STORAGE DEVICESSTORAGE DEVICES

HARD DISK :HARD DISK : It a device fixed to It a device fixed to a computer and can store large a computer and can store large volumes of information. It uses volumes of information. It uses magnetic media and electro magnetic media and electro magnetic theory to read and magnetic theory to read and store information. store information.

The standard capacity : 10 – 20 The standard capacity : 10 – 20 GBGB


FLOPPY DISK : FLOPPY DISK : It is a cassette like It is a cassette like device to store information. It is device to store information. It is external to a computer and can be external to a computer and can be put into a floppy disk drive (FDD) put into a floppy disk drive (FDD) attached to a computer for reading attached to a computer for reading and writing information. It also and writing information. It also uses electro magnetic theory. uses electro magnetic theory.

Since it is not fixed to a computer, Since it is not fixed to a computer, information can be copied from the information can be copied from the hard disk of a computer to a floppy hard disk of a computer to a floppy and can be used in another and can be used in another computer.computer.

Standard capacity : 1.44 MBStandard capacity : 1.44 MB


CD :CD : It stands for COMPACT DISK. It It stands for COMPACT DISK. It is the same as any other music or is the same as any other music or video CD. It is also external to a video CD. It is also external to a computer and can be put into a CD computer and can be put into a CD drive attached to a computer for drive attached to a computer for reading information. It uses reading information. It uses OPTICAL technology to read OPTICAL technology to read information. information.

Information once written into a CD Information once written into a CD can not be erased or changed. can not be erased or changed. Hence it is called a ROM (Read Only Hence it is called a ROM (Read Only Memory).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 thin The Compact Disc itself is a thin plastic disk some 12 cm. in plastic disk some 12 cm. in diameter. diameter.

Information is encoded in a Information is encoded in a plastic-encased spiral track plastic-encased spiral track contained on the top of the disk. contained on the top of the disk.

The spiral track is read optically The spiral track is read optically by a noncontact head which scans by a noncontact head which scans approximately radially as the disk approximately radially as the disk spins just above it. spins just above it.


MEMORYMEMORY : There are two types : There are two types of memory : RAM & ROM.of memory : RAM & ROM.

RAMRAM : Random Access Memory. : Random Access Memory. It is the main memory of the It is the main memory of the computer. It is volatile memory computer. It is volatile memory and the information gets erased and the information gets erased whenever the power supply is whenever 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 Information is burnt into the ROM chip at the time of ROM chip at the time of manufacturing. It can not be manufacturing. It can not be erased or altered and fresh erased or altered and fresh information can not be written information can not be written into the ROM. The BIOS is into the ROM. The BIOS is stored on ROM because the stored on ROM because the user cannot disrupt the user cannot disrupt the information.information.BIOS : Basic Input Output System.

It contains some instructions It contains some instructions required internally by the required 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. It Central Processing Unit. It is also called the micro is also called the micro processor.processor.There are CPUs with varying There are CPUs with varying efficiency and the quality of the efficiency and the quality of the computer depends mainly on computer depends mainly on the CPU present on the main the CPU present on the main board.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 main The main circuit board housing the circuit board housing the microprocessor, RAM, ROM and microprocessor, RAM, ROM and connecting interfaces to the connecting interfaces to the various other devices and various other devices and peripherals.peripherals.



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


A DESKTOP PERSONAL A DESKTOP PERSONAL COMPUTERCOMPUTER


SOFTWARE :SOFTWARE :

A set of programs that utilises A set of programs that utilises the hardware and uses its’ the hardware and uses its’ capabilities to perform various capabilities to perform various tasks.tasks.

ProgramProgram : A program is a set of : A program is a set of instructions stored in the instructions stored in the computer to solve specific computer to solve specific problems.problems.


CL ASS IF ICAT ION OF SOFT WARE

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


OPERATING SYSTEM : Programs OPERATING SYSTEM : Programs to control the hardware and to control the hardware and provide user interface. It is provide 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 level level language to low level language and vice-versa.language and vice-versa.

LOW LEVEL LANGUAGELOW LEVEL LANGUAGE : The : The language of bits understood language of bits understood directly by the computer. It is directly by the computer. It is also called the machine also called the machine language.language.HIGH LEVEL LANGUAGEHIGH LEVEL LANGUAGE : The : The language of users understood language of users understood by the computer only after by the computer only after translation.translation.


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


There are many languages and There are many languages and any one can be used to develop any one can be used to develop programs.programs.

Each language has it’s Each language has it’s capabilities and limitations.capabilities and limitations.

COBOL Commercial applications

BASIC Beginners’ language

FORTRAN

Mathematical and scientific applications

C System level programming


There are two types of There are two types of translators :translators :

INTERPRETER & COMPILER.INTERPRETER & COMPILER.An interpreter takes one An interpreter takes one instruction at a time, translates instruction at a time, translates it and moves on to the next it and moves on to the next statement in the program. statement in the program. Hence, executing the entire Hence, executing the entire program step by step.program step by step.

Each time we execute a Each time we execute a program the source program program the source program and the interpreter, both are and the interpreter, both are required.required.


A compiler takes all the high A compiler takes all the high level language instructions at a level language instructions at a time and creates a time and creates a corresponding machine corresponding machine language program which can be language program which can be directly executed by the directly executed by the computer. Hence, after computer. Hence, after compilation neither the source compilation neither the source program nor the compiler program nor the compiler program is required.program is required.

HIGH LEVEL

LANGUAGE

PROGRAM

MACHINE LANGUAG

E PROGRA

M

TRANSLATION &

COMPILATION


APPLICATION SOFTWARE :APPLICATION SOFTWARE :

These are programs developed These are programs developed using one of the languages to using one of the languages to perform a specific task.perform a specific task.


READY MADE :READY MADE :

These are programs developed These are programs developed by software companies for by software companies for general purpose applications. general purpose applications. These programs can be bought These programs can be bought and can be installed in the hard and can be installed in the hard disk of a computer.disk of a computer.

Examples : MS-WORD, FACT, Examples : MS-WORD, FACT, TALLY, FOXPRO etc.TALLY, FOXPRO etc.


CUSTOMISED OR TAILOR MADE :CUSTOMISED OR TAILOR MADE :

These are programs developed These are programs developed for SPECIFIC USER for SPECIFIC USER REQUIREMENT within an REQUIREMENT within an organisation. These programs organisation. These programs are developed by programmers are developed by programmers as per the user requirements.as per the user requirements.

Examples : Mark-sheet, Salary, Examples : Mark-sheet, Salary, Sales information, Railway Sales information, Railway reservation etc. reservation etc.


MS-DOSMS-DOS

Microsoft Microsoft

Disk Operating SystemDisk Operating System


FILE :FILE :Related information or data is Related information or data is stored in the form of a file in stored in the form of a file in the disk. Hence, the minimum the disk. Hence, the minimum chunk of information that we chunk of information that we can store in or retrieve form a can store in or retrieve form a disk, is a file.disk, is a file.

The files are either program The files are either program files or data files.files or data files.


Each file must have a unique Each file must have a unique name.name.

The file name has two parts :The file name has two parts :

PRIMARY NAMEPRIMARY NAME & &

SECONDARY NAME SECONDARY NAME oror extension.extension.The primary name is to The primary name is to identify the contents and the identify the contents and the extension is to identify the extension is to identify the type of the file.type of the file.


The primary file name can The primary file name can be maximum 8 characters be maximum 8 characters long.long.

The extension of the file The extension of the file name can be maximum 3 name can be maximum 3 characters long.characters long.

The primary file name and The primary file name and the extension is joined by a the extension is joined by a period.period.

The extension is optional.The extension is optional.


Legal characters in the file Legal characters in the file names include all letters of the names include all letters of the alphabet, numeric digits and alphabet, numeric digits and punctuation marks punctuation marks except the following characters : :

* ? = + | : [ ] ; , / \ < > “* ? = + | : [ ] ; , / \ < > “

A blank space A blank space can notcan not be used be used in the file name.in the file name.

Capital & small letters are Capital & small letters are treated as the same.treated as the same.


BIODATA.TXTSALARY.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 The wild card allows us to deal with more than one file at a time with more than one file at a time and helps us to group the files.and helps us to group the files.

** A substitute at the beginning A substitute at the beginning

? A substitute at specific positions? A substitute at specific positions


*.TXTPrimary name – anything

Extension - .TXT

BIODATA.TXTBOOK.TXTNOTES.TXT

SALARY.*Primary name – SALARY

Extension - anything

SALARY.98SALARY.DATSALARY.DOC

A*.*Primary name – starting with A


ALASKA.DOCABC.123

A

*.*Primary name – anything


All files

*.Primary name – anything

Extension – nothing (must not be there)

SALARYBIODATA

123


?A*.TXTPrimary name – second character A

Extension - .TXT

SALARY.TXTDATA.TXTRANA.TXT

*.?O?Primary name – anything

Extension – second character O

SALARY.DOCCOMMAND.COM

NOTES.SOS


DRIVE NAMESDRIVE NAMES

A computer can have more than A computer can have more than one disk drives like hard disk, one disk drives like hard disk, floppy disk drive & CD-rom floppy disk drive & CD-rom drive.drive.

Each of these drives are Each of these drives are identified by an alphabet and a identified by an alphabet and a colon symbol as A:, B:, C: etc.colon symbol as 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 The booting takes place with the help of instructions in the the help of instructions in the ROM.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 necessary DOS program files necessary for booting :for booting :

IO.SYSIO.SYSResponsible for the INPUT / OUTPUT operations

MSDOS.SYSMSDOS.SYSResponsible for the DISK & FILE operations

COMMAND.COMCOMMAND.COMActs 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:)


SOME ELEMENTARY DOS COMMANDS:SOME ELEMENTARY DOS COMMANDS:

CLSCLS

This command clears the screen This command clears the screen and takes the prompt to the and takes the prompt to the left-top corner of the screen.left-top corner of the screen.


DATEDATE

To change the system date.To change the system date.

On typing this command the On typing this command the current date is displayed and the current date is displayed and the user is allowed to type in the new user is allowed to type in the new date.date.


TIMETIME

To change the system time.To change the system time.

On typing this command the On typing this command the current time is displayed and the current time is displayed and the user is allowed to type in the new user is allowed to type in the new time.time.


DIRDIR

This command gives a listing, This command gives a listing, called the directory, of the files called the directory, of the files stored on a disk. stored on a disk.

It displays :It displays :•file namesfile names

•SizeSize

•date & time when the file was created or date & time when the file was created or updated.updated.



Options with DIROptions with DIR

DIR /PDIR /P Pause after every screen full of Pause after every screen full of information.information.DIR /WDIR /W Wide format displaying only the file Wide format displaying only the file names.names.DIR /ON DIR /ON In order of file name.In order of file name.

DIR /OE DIR /OE In order of extension.In order of extension.

DIR /OS DIR /OS In order of size.In order of size.

DIR /OD DIR /OD In order of date.In order of date.


Wild cards can be used with DIR Wild cards can be used with DIR to display a group of files to display a group of files satisfying the wild card criteria.satisfying the wild card criteria.

DIR *.TXT DIR *.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 The directory of another drive can be displayed by specifying the be displayed by specifying the drive name with the command.drive name with the command.

DIR A: DIR A: Displays the directory of the floppy in Displays the directory of the floppy in drive A.drive A.


BASIC FILE COMMANDSBASIC FILE COMMANDS

COPY COPY Make copies of files.Make copies of files.

SYNTAXSYNTAX

COPY [SOURCE] [TARGET]COPY [SOURCE] [TARGET]The source has to be a file name or wildcard The source has to be a file name or wildcard specification. It may or may not have a drive name. specification. It may or may not have a drive name. It it does not have a drive name, the file(s) is It it does not have a drive name, the file(s) is collected from the default drive.collected from 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 Copies the files with extension .TXT from the default drive ( C: ) to A:default drive ( C: ) to A:


C:\>COPY A:SALARY.DATC:\>COPY A:SALARY.DATCopies 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 In this case, since the target is the default drive it may not be written in the command.may not be written in the command.

C:\>COPY A:*.* B:*.*C:\>COPY A:*.* B:*.*Copies all files the first floppy drive to the second Copies all files the first floppy drive to the second floppy drive. floppy drive.

In this case, the current or the default drive is not In this case, the current or the default drive is not at all involved in the copying.at all involved in the copying.


While making a copy of a file we While making a copy of a file we can also change the name of the can also change the name of the file.file.

C:\>C:\>COPY MYFILE.TXT COPY MYFILE.TXT A:YOURFILE.TXTA:YOURFILE.TXTCopies the file from the default drive ( C: ) to A: Copies the file from the default drive ( C: ) to A: and the name of the file in drive A: changes.and the name of the file in drive A: changes.


We can make copies of the files in We can make copies of the files in the same disk also. But, while the same disk also. But, while copying in the same disk, the copying in the same disk, the name of the target file must be name of the target file must be specified as different than the specified as different than the source file.source file.

C:\>C:\>COPY STUDENT.DOC PUPIL.DOCCOPY STUDENT.DOC PUPIL.DOC

C:\>C:\>COPY *.TXT *.DOCCOPY *.TXT *.DOC


COMBINE THE CONTENTS OF COMBINE THE CONTENTS OF SEVERAL FILES INTO ONE FILE :SEVERAL FILES INTO ONE FILE :

COPY POEM1.TXT+POEM2.TXT COPY POEM1.TXT+POEM2.TXT POEM3.TXTPOEM3.TXT

This will combine the contents of This will combine the contents of the files POEM1.TXT & POEM2.TXT the files POEM1.TXT & POEM2.TXT and create a new file named and create a new file named POEM3.TXT.POEM3.TXT.


DELETING FILES:DELETING FILES:

Files can be removed one at a time or Files can be removed one at a time or several files at a time by using wild several files at a time by using wild cards. The commands are DEL or cards. The commands are DEL or ERASE. ERASE. DEL BIODATA.DOC DEL BIODATA.DOC Deletes the file Deletes the file BIODATA.DOC.BIODATA.DOC.

DEL *.txt DEL *.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 used The 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.00The name of the file STUDENT.99 changes to The name of the file STUDENT.99 changes to STUDENT.00STUDENT.00

REN *.99 *.00REN *.99 *.00The 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.TXTThis will display the contents of the file This will display the contents of the file BIODATA.TXTBIODATA.TXT

Wild card can not be used with this Wild card can not be used with this command, hence only one file can be command, hence only one file can be displayed at a time using the TYPE displayed at a time using the TYPE COMMAND.COMMAND.

TYPE displays the contents of text TYPE displays the contents of text files only.files only.


CREATE A SMALL TEXT FILE USING CREATE A SMALL TEXT FILE USING COPY :COPY :

COPY CON NEWFILE.TXTCOPY CON NEWFILE.TXT

The cursor comes to the next line and we can The cursor comes to the next line and we can enter the text line after line. On completion of enter the text line after line. On completion of typing use ctrl+Z to store the file.typing use ctrl+Z to store the file.


A sub-directory is a separate storage A sub-directory is a separate storage location in the disk where files can be location in the disk where files can be stored. This helps us to organise the files stored. 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 a There can be several subdirectories in a disk and the subdirectories are named the disk 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 called The first directory that is always there in a disk is called

the the rootroot directory. All other directories are created directory. 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 starts The 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

\

\STUDENT \ACCOUNT \TEXT \OTHER

\STUDENT\MARKS \TEXT\LETTER


ROOT


MARKS LETTER

CREATING SUB-DIRECTORIES

Command : MD or MKDIR

MD \STUDENTMD \ACCOUNT

MD \TEXT

MD \OTHERMD \STUDENT\MARKS

MD \TEXT\LETTER


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:\STUDENT\MARKS>=

C:\STUDENT\MARKS>CD \OTHER

C:\OTHER>=

C:\OTHER>CD \

C:\>=


COPYING FILES :

C:\>COPY \STUDENT\NOTES.TXT \TEXTCopies the file NOTES.TXT from the sub-directory STUDENT to TEXT

C:\>COPY \STUDENT\NOTES.TXT \TEXT

SUB-DIRECTORIES

FILE


MORE EXAMPLES :

C:\>COPY \OTHER\*.* \ACCOUNTCopies 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 \STUDENT\MARKSCopies all the files from the root directory to the sub-directory MARKS

C:\>COPY \TEXT\LETTER\*.* A:Copies all files from the sub-directory LETTER to the drive A


ROOT


MARKS LETTER

REMOVING SUB-DIRECTORIES

Command : RD or RMDIR

DEL \STUDENT\MARKS\*.*

RD \STUDENT\MARKS

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.


TREE TREE - 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.

Education

Introduction to computers