Computer Virus

A program which is written to cause problem in the computer in known as computer virus. Due to virus data may be corrupted or lost. A virus is commonly transferred through computer to computer on floppy disk or over a telephone link. Virus can be stop by using special anti-virus software.
A program that attempts to spread from computer to computer and either cause damage or annoy users by printing messages or altering what is displayed on the screen. When a program is inserted into another program then it is known as a computer is attacked by virus. It replicates itself and spread to another computer through floppy, mail and shared media. When the user run the infected program then it get chance to replicates itself.
Computer virus does not allows computer to run smoothly. Frequently computer hangs. It can also infect disk by attaching themselves to special programs in area of your disk called boot records and master boot records. Due to the virus computer may not boot and the size of the files changed automatically. Some of the names of computer virus are: C-Brain, Macmag Stores, Cascade, Jerusalem, Internet, Patch COM, Bomb, Macro virus etc.

Hardware, System Software & Application Software

The hardware cannot do anything without the software control. A computer will run only if mechanisms are provided th handle files, launch programs and deals with other user requests. These functions are carried out by system software called operating system. It is executed ta startup time and run constantly while the computer is on. The operating system instructs the computer on how to operate properly and manages the To and For flow of data from each part of the computer. It tends to isolate the hardware from the user, An operating system helps people use computer in many ways. But the functions performed by an OS are generally transparant or invisible to the users, eg: MS-DOS, OS/2, Windows, (95/98/2000/xp), Linus, UNIX etc.

An operating system is the program that, after being initially loaded into the computer, controls the execution of computer program and which may provide scheduling, debugging, Input/Output control, compilation, storage supervision and management of data etc. The operating system provides many important function to the people using the computer. From the largest mainframes and super computers to the small personal computer almost all computer system run under OS control.

As computer conisists of various resourceslike memory, CPU, Disk etc. It is very difficult for the user of computer to understand how to operate them directly. So OS becomes the interpreter between the computer hardware and users. It interprets the command of user to the hardware. For example, if we want to save our Bio-data in floppy disk, then we don't know "how to wright" or "where to write" inside the floppy, but our duty is simply t o give command to the operating system and then it will be the job of OS to tell the floppy drive what to do exactly. In short, OS acts as a interface and hides every details of working principle of computer from the user.

Memory

Memory is the place where we can store or hold the data and instruction for further operation. Memory stores three basic items: The operating system and other system software that control the usage of the computer equipment and application programs designed to carry out a specific task such as word processing and the data being processed by application programs. It is the storage area where the data are stored temporarily or permanently as per the need. Basically we have two types of memory; internal memory is simply called main memory or primary memory and the external memory called secondary memory or auxiliary memory or backup storage devices.

• Primary memory (Main memory)

Primary memory is the working space for the computer's processor. It is an area where the program and data being operated on by the processor must reside. It is used when small amount of data have to be exchanged quickly and used repeatedly. It allows CPU to store and retrieve data quickly.

• Secondary memory (Auxiliary storage or Secondary storage)

It is non-volatile memory that is stored externally to the computer. It is usually used for the storage of large amounts of data for permanent or long term storage of data or programs. Though, the secondary storage can hold much more data than primary storage, access to the data is slower. Only the programs and data currently needed by the processor reside in main memory. Normally, all other information is stored in secondary storage and is transferred to main memory when needed.

Levels of Hardware

1. Machine Level: Several hardware levels are presented in machine level. These are the basic elements of computer. They are processer, input/output, main device, axuiliary storage etc. This is top level of hardware in the hardware hierarchy where user can interact with them directly.
2. Micro Progaram Level: A sequence of microinstruction constitutes the micro program. The micro program is permanently stored in Read Only Memory(ROM) and normally cannot be changed. The Program in the permanent storage is called firmwarm. micro program are written for the control unit of the modern microprocesser. each computer instruction as actually accomplished by the execution of the related micro instruction in the micro program level.
3. Digital Logic Level: Almost all basic operation of the machine are provided at this level. The basic element at this level can store, manipulate and transmit data in the form of simple binary representations. These digital logic elements are called gates. A gates is normally constricted from small number of transistors and other electronic components. Many gates are combined together to form computer subsystems like adder, subtracter, multiplexer, decoder etc in a simple IC form or in multiple IC form. The standard digital logic devices are combined together to form computer processer or computer memories.
4. Electrical and Electronic Component Level: Almost all modern computer devices are built from simple electronic components such as diode, transistors, capacitors, registor or other components in integratedcircuits (IC) form. These components rely on suitable power supplies and operating environment.

Networking and Its Types

Networking is a collection and rearrangement of intelligent and distributed machine that shares data and information through lines of communication. It is very important concept to communicate from one place to another place. It is also defined as the connection of computer's pheripheral devices with cables oe even without cables (communication madia).
Types of Networking

1. LAN (Local Area Networking): This is the networking within a very limited area like a single building, within a college. LAN refers to a combination of hardware and transmission media. If computers are connected near to ech otherwith a communication media is called LAN. Due to the use of one kind of cable i.e. communication media, this is comparatively faster. It is limited generally upto 2 KM. The most important components in LAN are File server and OS (operating system).

2. MAN (Metropolitan Area Networking): When LAN grows and spread in area then it becomes MAN. It is also extended upto a city or a large geographical area. It comprises a combination of different hardware and transmission media. They are slower than LAN. The two important components of MANs are Security and Standarization.

3. WAN (Wide Area Networking): A wide area network is simple as LAN & MANs. WANs connect LANs that may be an opposite side of building, across the country of around the world. WANs can be characterized as either enterprises oe Global WANs. An enterprise WAN connects ars entire organization including all LANs at various site. Where as Global WANs also span the world but they do not have to connect LANs with in a single organization. The internet is an example of Global WAN.

Operator and its Types

Operator is a symbol that can perform mathematical or logical operation by using operands. eg: +, -, <, >etc.
Types of Operators

*Arithematical Operators (Binary): The operators that can perform simple arithematical calculation such as addition(+), substraction(-), multiplication(*) etc are known as arithematical operator.

*Relational Operator: The operators that are used to compare the expression are called relational operation. less than(<), greater than(>), less than or equal to(<=), not equal to(!=) are some of the examples of relational operator. *Logical Operator: The operators that are used to give logical value either true or false are called logical operator. logical AND(&&), logical NOT(!) are the example of logical operator.

*Unary Operator: The operators that are used to increase or decrease the value by one is called unary operator. ++, -- are the example of this operator

*Assignment Operator: It is used to assign the value of expression into variable. This operator is denoted by =.

*Short Hand Operator: It is the Combination of Arithematic and Assignment operators. At first it perform arithematic operator then assignment operator. example: +=, -=, *= etc.

*Conditional: It is written is the form, exp1?statement1:statement2; where, the value of exp1 is evaluated. If it is true statement1 is executed other statement2 is exicuted.

*Bitwise Operator: It is used to Perform operation in bit level, that is used for logical operations in bit level.

*Comma Operator: This operator is used to join two expression. This operator is denoted by (,)

History and Introduction of C Language

It is a Language of computer that was developed by Dennis Ritch in 1970 at AT and Bell Labrotary of US. It is a kind of high level language but has also the feature of machine level language. So, that it is a intermediate language between high level language and machine level language. It is used to write system software as well as application software. The strength of C language is very popular because all types of software ade developed by using C programming language.

Features:

• It is structure programming language. (used of if, for)
• The program is divided into number of functions.
• It has its own syntax to write a program.
• It has some keywords and functions to write a program as if, else, for case etc
• The compiler of of this language is easier installed on every computer.

History of The Computer

History of the computer starts from the time when there were no any number system discovered for calculation. As an when men face problem, then begins the development of computer.

• Abacus.

It is an earliest counting device. It is a rectangular shape box having two parts and divided by Mid-bar , upper part is called Heaven consists of 2 beads and equal to value 5 and lower part is called Earth consists of 5 beads and each beads equals to value 1. While calculating beads are brought near to the midbar. It could only do addition and subtraction. It is belived to discovered in China, Russia or Egypt.

• Slide Ruler.

An english mathematican Williem Oughtred discovered a device with 2 rulers for calculation which was based on John Napiers principle which was called Slide Ruler. This device could perform multiplication and division. It was the first analog device.

• Pascaline.

In 1642 A.D. the first mechanical calculating machine begun to design by a French Mathematican named Blaise Pascal. This machine can add or subtract upto 8 column numbers. This machine can only add and subtract, not more than that.

• Leibniz's Calculating Machine.

In 1671 A.D. a new machine was developed by a Gedrman Philosopher Gottfried Von Leibniz which can perform addition, subtraction, multiplication, division and to calculate the square roots. It was the first machine to calculate all these arithematic calculation automatically.

• Charles Babbage Engine.

In 1823 A.D. an English Mathematician (Professor of MAthematics at Cambridze University) developed a machine called Difference Engine with Mechanical memory to store result. After sometime he developed a bigger machine called Analytical Engine in 1830 A.D. which could compute upto 20 decimal places. He (Charles Baggage) inventd the principle in which modern computer works, so he is known as "Father of Computer Science". Using his this principle about 100 years later, Mark-1, was developed by Howard Aiken in 1937.

Computer

Computer is a automatic electronic device which takes input from input device like keyboard, mouse and process through processer i.e. central processing unit (CPU), give output through monitor and store the data and information for future use. The development of computer did not get at once, when an ever people feels difficult in calculating or counting the device, then it begins to developed.

Every thing have it merits and demerits, like wise computer also have its advantages and disadvantages. The advantages of computer are:

• It is used in different field like in research, designing, study etc.
• It keeps the data and information for future purposes which will be difficult for human being to remember.
• It can also used in entertainment purpose like listening songs, chatting, mailing and many more

The disadvantages of computer are:

• It is a electronic device so frequent maintaince is to be done.
• To run the computer well trained manpower is needed.
• It is more expensive so everyone can't afford it.