MTA – (II) ( 12) : ELECTRONIC DATA PROCESSING- module 2

Module – 2 : File Organisation and Processing: Fields, Records, Files, Type of files, Serial,

Sequential, Index Sequential and Random files, File Organisations, Batch Processing, Real time

processing, Time sharing, Multi Processing, Multi Programming, Client Serves processing.

Fields: A field in Microsoft Access is a piece of information related to a single person or thing. Related fields are grouped together to form a record.

Records: In a database, a record (sometimes called a row) is a group of fields within a table that are relevant to a specific entity. For example, in a table called customer contact information, a row would likely contain fields such as: ID number, name, street address, city, telephone number and so on

Files:

A file is a logical collection of information stored on secondary storage such as hard disk. Physically, a file is the smallest allotment of secondary storage devices e.g. disk. Logically, a file is a sequence of logical records i.e. a sequence of bits and bytes. Files can be used to contain data and programs (both source and object program). Data files can be numeric, alphabetic, alphanumeric or binary. A file has various attributes like name, type, location, size, protection, time and date of creation etc.

Type of files:

In order to support different types of files, operating systems support two part file names. The two parts are: name and an extension. Both are separated by a period (dot). For example, a name of a file can be program C.

File Type	Extension	Meaning
Execute file	.exe, .com, .bin	Read to run machine language program
Object file	.obj, .o	Compiled, machine language but not linked
Source code file	.c, .cc, .java, .pas, .asm, .a, .ftn	Represents source code in different languages such as c, java, pascal, assembly language of fortran.
Batch file	.bat, .sh	Command to the command interpreter.
Text file	.txt, .doc	Documentation
Library file	.lib, .dll	Libraries of routines for programmers
Backup file	.bak	Used for taking backup of some program file
Multimedia file	.mpeg, .mov, .rm	Binary file containing audio or audio/video information

Access Methods:

Files are used to store data. The information present in the file can be accessed by various methods. Thus, the way of retrieving data from a file is known as access method. Different systems use different access methods. The various access methods used are:

1.      Sequential access

It is the simplest and most commonly used access method. Information in the file is accessed in the order it is stored in the file i.e. one record after the other. Starting at the beginning to the end of the file.

2.      Direct access

In direct access method it is possible to access the records of a file in any order. The various records can be read or write randomly. In this way the records can be accessed by key, rather than by position.

3.      Indexed access

In this method, an index is created for the file. This index contains pointer for various blocks of a file, just like a index in a back of a book. If we want to find a record of a file, first the index is searched and then the pointer from index is used to access that file. In this way, a required record is found.

File Organisations

It is used to determine an efficient file organization for each base relation. For example, if we want to retrieve student records in alphabetical order of name, sorting the file by student name is a good file organization. However, if we want to retrieve all students whose marks is in a certain range, a file ordered by student name would not be a good file organization. Some file organizations are efficient for bulk loading data into the database but inefficient for retrieve and other activities.

Types of File Organization

In order to make effective selection of file organizations and indexes, here we present the details different types of file Organization. These are:

 • Heap File Organization: An unordered file, sometimes called a heap file, is the simplest type of file organization.

Records are placed in file in the same order as they are inserted. A new record is inserted in the last page of the file; if there is insufficient space in the last page, a new page is added to the file. This makes insertion very efficient. 

• Hash File Organization: In a hash file, records are not stored sequentially in a file instead a hash function is used to calculate the address of the page in which the record is to be stored. The field on which hash function is calculated is called as Hash field and if that field acts as the key of the relation then it is called as Hash key.

• Indexed Sequential Access Methods (ISAM) File Organization: In an ISAM system, data is organized into records which are composed of fixed length fields. Records are stored sequentially. A secondary set of hash tables known as indexes contain "pointers" into the tables, allowing individual records to be retrieved without having to search the entire data set. It is a data structure that allows the DBMS to locate particular records in a file more quickly and thereby speed response to user queries. 

• B+- tree File Organization: B+-tree is a more versatile storage structure than hashing. It supports retrievals based on exact key match, pattern matching, range of values, and part key specification. The B+-tree index is dynamic, growing as the relation grows. 

• Cluster File Organization:

Some DBMSs, such as Oracle, support clustered and non-clustered tables. Clusters are group of one or more tables physically stored together because they share common columns and are often used together.

Indexed Clusters

In an index cluster, records with the same cluster key are stored together. Oracle suggests using indexed clusters when:

• Queries retrieve records over a range of cluster key value;

• Clustered tables may grow unpredictable.

Cluster can improve performance of retrieval, depending on the data distribution and what SQL operations are most often performed on the data

Hash Clusters

Hash clusters also cluster table data in a manner similar to index clusters. However, a record is stored in a hash cluster based on the result of applying a hash function to the record's cluster key value. All records with the same hash key value are stored together on disk.

Batch Processing: In Batch processing system, the various jobs of the users are collected in a queue. This process is known as spooling. SPOOLING is the short form of Simultaneous Peripheral Operations On Line.

Users didn’t interact directly with computer system; they prepare their job that consisted of the program, data and some control information. This job was usually in form of punched cards. The users submit then job to a computer operator. When batches of programs have been collected, the operator loads this batch of programs into the computer at one time where they are executed one after the other. Finally, the operators retrieve the output of these jobs and return them to the concerned users. In this way many different jobs are processed, one after the other without any interaction from the users during program execution.

1. ·        The batch processing operating system was called a monitor that resides in the main memory. Such a portion of main memory is known as resident monitor.
2. ·         The batch monitor executes batches of job at definite interval of time.
3. ·         The batch monitor accepts the commands for initializing, processing and terminating a batch.

 Real Time processing,

In a real time operating system, a job is to be completed within the rigid time constraints otherwise job loses its meaning. A real time system functions correctly only if it returns the correct result within its time constraints. Thus, in a real-time system, the correctness of the computation not only depends upon the logical correctness of the computation but also upon the time at which the result is produced. A real time system is often used as a central device in a dedicated application like fuel-injection system, robotics, air-traffic control and medical imaging systems, systems that control scientific experiment, industrial control system and weapon systems.

Time sharing

Time sharing refers to the allocation of computer resources in a time dependent fashion to several programs simultaneously. A time sharing system has many user terminals that are connected to same computer simultaneously. Using these terminals, different users can work on a system at the same time. In timesharing system, the CPU time is divided among all the users on a scheduled basis. Each user program is allocated a very short period of CPU time one-by-one, beginning from the first user program and proceeding the last one, and then again beginning from the first one. This short period of time during which user gets the attention of the CPU is known as a Time Slice. Time slot or Quantum. Thus, in timesharing, when the CPU is allocated to a user program, the user uses the CPU for the period of time slot. It releases the CPU under any of the following three conditions:-

1.      When the allotted time slice expires

2.      When the program needs to perform I/O operations.

3.      When the execution of the program is over during the time slice.

Even though it may appear that several users are using computer system at the same time, a single CPU system can only execute one instruction at a time. Thus, like multiprogramming, even with a timesharing system, only one program can be in control of the CPU at any given time.

Multi Processing

Multiprocessor system is the system that contains two or more processors or CPUs and has ability to simultaneously execute several programs. Hence, the name ‘multi-processor’.

In such a system, multiple processors share the clock, bus, memory and peripheral devices. A multiprocessor system is also known as parallel system.

                                                            In such a system, instructions from different and independent programs can be processed at the same instant of time by different CPUs.

In this system, the CPUs may simultaneously execute different instructions from the same program.

Multi Programming

Multiprogramming operating system allows multiple users to execute multiple programs using a single CPU concurrently i.e. at the same time. In multiprogramming several processes are kept in the main memory and CPU execute all these processes concurrently. It means, the CPU immediately switches from one process to next that are ready to be executed.

The advantages of Multiprogramming are:

1.      Increased throughput:

Throughput is increased by utilizing the idle-time of CPU for running other programs that are already present in the main memory.

2.      Lowered Response Rate:

Response time is lowered by recognizing the priority of a job as it enters the system and by processing a jobs on a priority basis.

3.      Ability to assign priorities to Jobs:

Most multiprogramming systems have schemes for setting priorities for rotating programs. They specify when the CPU will rotate to another program, and which program it will rotate to.

Client Server System

# Distributed System

A distributed system is a collection of processors located in geographical dispersed physical location. In this system, the workload is divided between two or more computers that are linked together by a communication network. That is, the different processors communicate using communication links, such as telephone lines and buses. The processors in a distributed system vary in size and function. They may include small microprocessors, workstations microcomputers, mainframe computers and large general purpose computers. The various processors are also called as sites, nodes, hosts or machine. The purpose of distributed system is to provide an efficient and convenient environment for sharing of resources.

MTA – (II) ( 12) : ELECTRONIC DATA PROCESSING- module 1

Module – 1: Introduction to Computer: Simple model of computer, generation of computers, computer Hardware/software concept,

Computer Fundamental: Numbering system and data representation, I/Q Devices, Memory devices, Programming, languages, CPU, Applications of computer.

Introduction to Computer:

A computer is an electronic data processing device, which accepts and stores data input, processes the data input, and generates the output in a required format.

The purpose of this tutorial is to introduce you to Computers and its fundamentals.

Functionalities of a Computer

If we look at it in a very broad sense, any digital computer carries out the following five functions −

Step 1 − Takes data as input.

Step 2 − Stores the data/instructions in its memory and uses them as required.

Step 3 − Processes the data and converts it into useful information.

Step 4 − Generates the output.

Step 5 − Controls all the above four steps.

Advantages of Computers

Following are certain advantages of computers.

High Speed

·        Computer is a very fast device.

·        It is capable of performing calculation of very large amount of data.

·        The computer has units of speed in microsecond, nanosecond, and even the picosecond.

·        It can perform millions of calculations in a few seconds as compared to man who will spend many months to perform the same task.

Accuracy

·        In addition to being very fast, computers are very accurate.

·        The calculations are 100% error free.

·        Computers perform all jobs with 100% accuracy provided that the input is correct.

Storage Capability

·        Memory is a very important characteristic of computers.

·        A computer has much more storage capacity than human beings.

·        It can store large amount of data.

·        It can store any type of data such as images, videos, text, audio, etc.

Diligence

·        Unlike human beings, a computer is free from monotony, tiredness, and lack of concentration.

·        It can work continuously without any error and boredom.

·        It can perform repeated tasks with the same speed and accuracy.

Versatility

·        A computer is a very versatile machine.

·        A computer is very flexible in performing the jobs to be done.

·        This machine can be used to solve the problems related to various fields.

·        At one instance, it may be solving a complex scientific problem and the very next moment it may be playing a card game.

Reliability

·        A computer is a reliable machine.

·        Modern electronic components have long lives.

·        Computers are designed to make maintenance easy.

Automation

·        Computer is an automatic machine.

·        Automation is the ability to perform a given task automatically. Once the computer receives a program i.e., the program is stored in the computer memory, then the program and instruction can control the program execution without human interaction.

Reduction in Paper Work and Cost

·        The use of computers for data processing in an organization leads to reduction in paper work and results in speeding up the process.

·        As data in electronic files can be retrieved as and when required, the problem of maintenance of large number of paper files gets reduced.

·        Though the initial investment for installing a computer is high, it substantially reduces the cost of each of its transaction.

Disadvantages of Computers

Following are certain disadvantages of computers.

No I.Q.

·        A computer is a machine that has no intelligence to perform any task.

·        Each instruction has to be given to the computer.

·        A computer cannot take any decision on its own.

Dependency

·        It functions as per the user’s instruction, thus it is fully dependent on humans.

Environment

·        The operating environment of the computer should be dust free and suitable.

No Feeling

·        Computers have no feelings or emotions.

·        It cannot make judgment based on feeling, taste, experience, and knowledge unlike humans.

#Simple model of computer

Generation in computer terminology is a change in technology a computer is/was being used. Initially, the generation term was used to distinguish between varying hardware technologies. Nowadays, generation includes both hardware and software, which together make up an entire computer system.

There are five computer generations known till date. Each generation has been discussed in detail along with their time period and characteristics. In the following table, approximate dates against each generation has been mentioned, which are normally accepted.

Following are the main five generations of computers.

S.No	Generation & Description
1	First Generation The period of first generation: 1946-1959. Vacuum tube based.
2	Second Generation The period of second generation: 1959-1965. Transistor based.
3	Third Generation The period of third generation: 1965-1971. Integrated Circuit based.
4	Fourth Generation The period of fourth generation: 1971-1980. VLSI microprocessor based.
5	Fifth Generation The period of fifth generation: 1980-onwards. ULSI microprocessor based.

Computer Hardware/software concept,

Computer Fundamental:

Numbering system and data representation,

When we type some letters or words, the computer translates them in numbers as computers can understand only numbers. A computer can understand the positional number system where there are only a few symbols called digits and these symbols represent different values depending on the position they occupy in the number.

The value of each digit in a number can be determined using −

·        The digit

·        The position of the digit in the number

·        The base of the number system (where the base is defined as the total number of digits available in the number system)

Decimal Number System

The number system that we use in our day-to-day life is the decimal number system. Decimal number system has base 10 as it uses 10 digits from 0 to 9. In decimal number system, the successive positions to the left of the decimal point represent units, tens, hundreds, thousands, and so on.

Each position represents a specific power of the base (10). For example, the decimal number 1234 consists of the digit 4 in the units position, 3 in the tens position, 2 in the hundreds position, and 1 in the thousands position. Its value can be written as

(1 x 1000)+ (2 x 100)+ (3 x 10)+ (4 x l)

(1 x 103)+ (2 x 102)+ (3 x 101)+ (4 x l00)

1000 + 200 + 30 + 4

1234

As a computer programmer or an IT professional, you should understand the following number systems which are frequently used in computers.

S.No.	Number System and Description
1	Binary Number System Base 2. Digits used : 0, 1
2	Octal Number System Base 8. Digits used : 0 to 7
3	Hexa Decimal Number System Base 16. Digits used: 0 to 9, Letters used : A- F

Binary Number System

Characteristics of the binary number system are as follows −

·        Uses two digits, 0 and 1

·        Also called as base 2 number system

·        Each position in a binary number represents a 0 power of the base (2). Example 2⁰

·        Last position in a binary number represents a x power of the base (2). Example 2^x where x represents the last position - 1.

Example

Binary Number: 10101₂

Calculating Decimal Equivalent −

Step	Binary Number	Decimal Number
Step 1	101012	((1 x 24) + (0 x 23) + (1 x 22) + (0 x 21) + (1 x 20))10
Step 2	101012	(16 + 0 + 4 + 0 + 1)10
Step 3	101012	2110

Note − 10101₂ is normally written as 10101.

Octal Number System

Characteristics of the octal number system are as follows −

·        Uses eight digits, 0,1,2,3,4,5,6,7

·        Also called as base 8 number system

·        Each position in an octal number represents a 0 power of the base (8). Example 8⁰

·        Last position in an octal number represents a x power of the base (8). Example 8^x where x represents the last position - 1

Example

Octal Number: 12570₈

Calculating Decimal Equivalent −

Step	Octal Number	Decimal Number
Step 1	125708	((1 x 84) + (2 x 83) + (5 x 82) + (7 x 81) + (0 x 80))10
Step 2	125708	(4096 + 1024 + 320 + 56 + 0)10
Step 3	125708	549610

Note − 12570₈ is normally written as 12570.

Hexadecimal Number System

Characteristics of hexadecimal number system are as follows −

·        Uses 10 digits and 6 letters, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

·        Letters represent the numbers starting from 10. A = 10. B = 11, C = 12, D = 13, E = 14, F = 15

·        Also called as base 16 number system

·        Each position in a hexadecimal number represents a 0 power of the base (16). Example, 16⁰

·        Last position in a hexadecimal number represents a x power of the base (16). Example 16^x where x represents the last position - 1

Example

Hexadecimal Number: 19FDE₁₆

Calculating Decimal Equivalent −

Step	Binary Number	Decimal Number
Step 1	19FDE16	((1 x 164) + (9 x 163) + (F x 162) + (D x 161) + (E x 160))10
Step 2	19FDE16	((1 x 164) + (9 x 163) + (15 x 162) + (13 x 161) + (14 x 160))10
Step 3	19FDE16	(65536+ 36864 + 3840 + 208 + 14)10
Step 4	19FDE16	10646210

Note − 19FDE₁₆ is normally written as 19FDE.

 I/Q Devices

I/O devices are the pieces of hardware used by a human (or other system) to communicate with a computer. For instance, a keyboard or computer mouse is an input device for a computer, while monitors and printers are output devices. Devices for communication between computers, such as modems and network cards, typically perform both input and output operations.

Following are some of the important input devices which are used in a computer −

• Keyboard
• Mouse
• Joy Stick
• Light pen
• Track Ball
• Scanner
• Graphic Tablet
• Microphone
• Magnetic Ink Card Reader(MICR)
• Optical Character Reader(OCR)
• Bar Code Reader
• Optical Mark Reader(OMR)

Keyboard

Keyboard is the most common and very popular input device which helps to input data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.

eyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.

The keys on the keyboard are as follows −

S.No	Keys & Description
1	Typing Keys These keys include the letter keys (A-Z) and digit keys (09) which generally give the same layout as that of typewriters.
2	Numeric Keypad It is used to enter the numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
3	Function Keys The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has a unique meaning and is used for some specific purpose.
4	Control keys These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
5	Special Purpose Keys Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.

Mouse

Mouse is the most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base, which senses the movement of the mouse and sends corresponding signals to the CPU when the mouse buttons are pressed.

Generally, it has two buttons called the left and the right button and a wheel is present between the buttons. A mouse can be used to control the position of the cursor on the screen, but it cannot be used to enter text into the computer.

Advantages

• Easy to use
• Not very expensive
• Moves the cursor faster than the arrow keys of the keyboard.

Joystick

Joystick is also a pointing device, which is used to move the cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.

The function of the joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games.

Light Pen

Light pen is a pointing device similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube.

When the tip of a light pen is moved over the monitor screen and the pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.

Track Ball

Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the pointer can be moved.

Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button, or a square.

Scanner

Scanner is an input device, which works more like a photocopy machine. It is used when some information is available on paper and it is to be transferred to the hard disk of the computer for further manipulation.

Scanner captures images from the source which are then converted into a digital form that can be stored on the disk. These images can be edited before they are printed.

Digitizer

Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at.

Digitizer is also known as Tablet or Graphics Tablet as it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for fine works of drawing and image manipulation applications.

Microphone

Microphone is an input device to input sound that is then stored in a digital form.

The microphone is used for various applications such as adding sound to a multimedia presentation or for mixing music.

Magnetic Ink Card Reader (MICR)

MICR input device is generally used in banks as there are large number of cheques to be processed every day. The bank's code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable.

This reading process is called Magnetic Ink Character Recognition (MICR). The main advantages of MICR is that it is fast and less error prone.

Optical Character Reader (OCR)

OCR is an input device used to read a printed text.

OCR scans the text optically, character by character, converts them into a machine readable code, and stores the text on the system memory.

ollowing are some of the important output devices used in a computer.

• Monitors
• Graphic Plotter
• Printer

Monitors

Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. The sharpness of the image depends upon the number of pixels.

There are two kinds of viewing screen used for monitors.

• Cathode-Ray Tube (CRT)
• Flat-Panel Display

Cathode-Ray Tube (CRT) Monitor

The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity or resolution. It takes more than one illuminated pixel to form a whole character, such as the letter ‘e’ in the word help.

A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes - fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically.

There are some disadvantages of CRT −

• Large in Size
• High power consumption

Flat-Panel Display Monitor

The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, and graphics display.

The flat-panel display is divided into two categories −

·        Emissive Displays − Emissive displays are devices that convert electrical energy into light. For example, plasma panel and LED (Light-Emitting Diodes).

·        Non-Emissive Displays − Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. For example, LCD (Liquid-Crystal Device).

Printers

Printer is an output device, which is used to print information on paper.

There are two types of printers −

• Impact Printers
• Non-Impact Printers

Impact Printers

Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper.

Characteristics of Impact Printers are the following −

• Very low consumable costs
• Very noisy
• Useful for bulk printing due to low cost
• There is physical contact with the paper to produce an image

These printers are of two types −

• Character printers
• Line printers

Character Printers

Character printers are the printers which print one character at a time.

These are further divided into two types:

• Dot Matrix Printer(DMP)
• Daisy Wheel

Dot Matrix Printer

In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in the form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character which is why it is called Dot Matrix Printer.

Advantages

• Inexpensive
• Widely Used
• Other language characters can be printed

Disadvantages

• Slow Speed
• Poor Quality

Daisy Wheel

Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower) which is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices that require a few letters to be sent here and there with very nice quality.

Advantages

• More reliable than DMP
• Better quality
• Fonts of character can be easily changed

Disadvantages

• Slower than DMP
• Noisy
• More expensive than DMP

Non-impact Printers

Non-impact printers print the characters without using the ribbon. These printers print a complete page at a time, thus they are also called as Page Printers.

These printers are of two types −

• Laser Printers
• Inkjet Printers

Characteristics of Non-impact Printers

• Faster than impact printers
• They are not noisy
• High quality
• Supports many fonts and different character size

Laser Printers

These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.

Advantages

• Very high speed
• Very high quality output
• Good graphics quality
• Supports many fonts and different character size

Disadvantages

• Expensive
• Cannot be used to produce multiple copies of a document in a single printing

Inkjet Printers

Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.

They make less noise because no hammering is done and these have many styles of printing modes available. Color printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also.

Advantages

• High quality printing
• More reliable

Disadvantages

• Expensive as the cost per page is high
• Slow as compared to laser printer

Memory Devices

A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer, where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.

Memory is primarily of three types −

• Cache Memory
• Primary Memory/Main Memory
• Secondary Memory

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.

Advantages

The advantages of cache memory are as follows −

• Cache memory is faster than main memory.
• It consumes less access time as compared to main memory.
• It stores the program that can be executed within a short period of time.
• It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

• Cache memory has limited capacity.
• It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

Characteristics of Main Memory

• These are semiconductor memories.
• It is known as the main memory.
• Usually volatile memory.
• Data is lost in case power is switched off.
• It is the working memory of the computer.
• Faster than secondary memories.
• A computer cannot run without the primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory

• These are magnetic and optical memories.
• It is known as the backup memory.
• It is a non-volatile memory.
• Data is permanently stored even if power is switched off.
• It is used for storage of data in a computer.
• Computer may run without the secondary memory.
• Slower than primary memories.

  ,

Programming languages,

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPUhas its own unique machine language. Lying between machine languages and high-level languages are languages called assembly languages. Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute namesfor numbers. Machine languages consist of numbers only. Lying above high-level languages are languages called fourth-generation languages (usually abbreviated 4GL). 4GLs are far removed from machine languages and represent the class of computer languages closest to human languages. Regardless of what language you use, you eventually need to convertyour program into machine language so that the computer can understand it. There are two ways to do this: 1) compile the program 2) interpret the program

CPU

Central Processing Unit (CPU) consists of the following features −

• CPU is considered as the brain of the computer.
• CPU performs all types of data processing operations.
• It stores data, intermediate results, and instructions (program).
• It controls the operation of all parts of the computer.

CPU itself has following three components.

• Memory or Storage Unit
• Control Unit
• ALU(Arithmetic Logic Unit)

Applications of computer

Here is a list of some of the most prominent features of a system software −

• Close to the system
• Fast in speed
• Difficult to design
• Difficult to understand
• Less interactive
• Smaller in size
• Difficult to manipulate
• Generally written in low-level language

Application Software

Application software products are designed to satisfy a particular need of a particular environment. All software applications prepared in the computer lab can come under the category of Application software.

Application software may consist of a single program, such as Microsoft's notepad for writing and editing a simple text. It may also consist of a collection of programs, often called a software package, which work together to accomplish a task, such as a spreadsheet package.

Examples of Application software are the following −

• Payroll Software
• Student Record Software
• Inventory Management Software
• Income Tax Software
• Railways Reservation Software
• Microsoft Office Suite Software
• Microsoft Word
• Microsoft Excel
• Microsoft PowerPoint

Features of application software are as follows −

• Close to the user
• Easy to design
• More interactive
• Slow in speed
• Generally written in high-level language
• Easy to understand
• Easy to manipulate and use
• Bigger in size and requires large storage space

Business

A computer has high speed of calculation, diligence, accuracy, reliability, or versatility which has made it an integrated part in all business organizations.

Computer is used in business organizations for − Payroll calculations, Budgeting, Sales analysis, Financial forecasting, Managing employee database, Maintenance of stocks, etc.