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What computers can do?

6:42 PM kdhakal 1 comments
Computers can perform a wide range of operations. As a matter of fact, in today's competitive world, one cannot think of doing anything without the help of the computers. From household to offices, department stores and shopping malls, computers have prevailed everywhere.


A Laptop Computer


What can you do with computers?
People use computers to keep and analyze records, manage researches and projects etc in the workplace. At home, computers can be used to find information, store various data like pictures, music and videos, track finances, play games, communicate with other people around the world via the internet and much more. With Internet access, you can communicate with people all over the world and find a vast amount of information.

 

What is web?

The World Wide Web (usually called the web, or web) is a vast storage of information. The web displays most of the information in a visually delightful format, hence the reason for its popularity. Headlines, text, and pictures can be combined on a single webpage; similar to the pages in a magazine, along with sounds and videos. A website is a collection of interconnected webpages. The web contains millions of websites and billions of webpages, and millions of websites are uploaded each day.


Example of a webpage (facebook.com)
Example of a webpage (facebook.com)


Exploring the web is known as Surfing. Anyone surfing the web can find information about almost anything or any topic imaginable. You can read news or stories and movies reviews, book a hotel or an air ticket, view maps, get current weather and future weather forecast, view pictures or videos, play games or read the game reviews, etc. Almost all the companies, agencies, libraries and museums today have their own websites with information about their products and services or collections. You can also search and purchase products online - books, music, toys, clothing, electronics, and much more. You can also buy and sell used items through websites that use auction-style bidding. For example, see this website.

 

E‑mail

E‑mail (Electronic mail) is an electronic means of sending the letter to someone. When you send an e‑mail message, it arrives almost instantly in the recipient's e‑mail inbox. E-mail messages can be sent to many people simultaneously,  and you can save, print, and forward the e‑mail to others. You can send almost any type of file in an e‑mail message; documents, pictures, music, videos etc. And with e‑mail, you don't need a postage stamp (how cool is that!!).

 

Instant messaging

Instant messaging is having a real - time conversation with another person who is far away from you. When you send an instant message, the message is immediately visible to all participants of the conversation. Unlike e‑mail where the message is delivered at any time and the recipient may view it at anytime, for instant messaging, all participants of the conversation have to be online (connected to the Internet) and in front of their computers at the same time. Communicating by means of instant messaging is also known as chatting.

 

Pictures, music, and movies

If you have a digital camera, you can move your pictures from the camera to your computer. Then you can print them, create slide shows, or share them with others by e‑mail or by posting them on a website. You can also listen to music on your computer, either by importing music from audio CDs or by purchasing songs from a music website. Or, you can tune in to one of the thousands of radio stations that broadcast over the Internet. If your computer comes with a DVD player, you can watch movies too.

 

Gaming

Everybody likes to play games. There are thousands of computer games in every category imaginable, which you can play on your computer. Get behind the wheel of a over-speeding car, battle frightening monsters in a dungeon, or control civilizations and empires! Many games allow the users to compete with other players around the world via the Internet.
There are also some games which can be played online only - called online games. Such games can be played with the computer or with other opponents from around the world. You can also earn money from these games if you win or even if you are close to win!


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Inside the computer

7:06 PM kdhakal 1 comments
Whats inside the computer?

Following picture shows a view of the inner organs of a computer.



Inside the computer
Insde a typical computer


Power Supply:

Power supply
Power supply
A power supply or SMPS (Switched Mode Power Supply) converts AC signal to low voltage regulated DC signal for the use of components inside the computer. Most modern desktop computer power supplies are ATX power supplies, which always provides a 5 V voltage although it is connected to the mains supply. ATX power supply can be turned ON and OFF by a signal from the computer.


Processor:




Processor Fan. The actual processor is below this fan
Processor


     A processor is a multipurpose, programmable device that takes data from the user, processes it according to the instructions stored in its memory, and gives the result of the processing as output. In the earlier days of computer history, processors were constructed in small and medium scale IC forms, consisting of tens to few hundred transistors. Such processors were too much limited in their operations, and power consumption was also high. The first processors appeared in early 1970s, which were used for digital calculators, terminals, printers and other simple type of automatic systems.
intel 4004 processor
intel 4004 processor

     The first commercial processor was intel 4004, whose price was $60. It was originally designed by intel for desktop calculators for a Japanese calculator company, with high performance and rich features. It was a 4-bit processor, with a clock speed of 740 kHz. Since the intel 4004, the history of processors has undergone a vast improvement in size, performance, quality, power consumption, etc. and today we have intel i7 the most advanced processor up to date.


Modern Processor




Hard disk:


Hard disk
Hard Disk
A hard disk drive is a data storage device for a computer. It is used for storing the digital information processed by the computer for later use. A hard disk usually consists of rapidly rotating disks (or "plates") which are coated with magnetic material so that data can be stored in digital form. The magnetic storage of digital data is not deleted even when the power to the disk is cut off because data is stored as "magnetic cells" on the surface of the disk plates.




A simple hard disk
A simple hard disk





Exploded view of a hard disk
Exploded view of a hard disk





PCI Slots:

PCI Slots
PCI Slots


PCI (Peripheral Components Interconnect) are the slots on a motherboard where extra components in a computer can be inserted. It is a type of bus; the terminal where other components are inserted.
If, for example, you want to insert a TV card (a device that allows to watch TV on your PC), which does not usually come with your computer, you can insert it in the PCI bus and watch TV. Modems and NICs (Network Interface Card) are other devices that are usually inserted in a PCI slot.


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OSI Model (contd ...)

1:44 PM kdhakal 1 comments
 Transport layer

The transport layer provides the flow of data between computers, as the name suggests. The Transmission Control Protocol, TCP and the User Datagram Protocol reside in this layer. In the transport layer, the data is segmented into parts to achieve a steady flow so that the differences in connection bandwidth between the host computers does not matter in the circulation of the data through the network.

Network layer
The Network Layer helps in transporting the data between the networks. At the beginning of the segments a network header is placed, which consists of the IP addresses of the sender and the receiver terminals. This header remains constant which is just read during the process of communication. The IP or Network trailer is also present at the end of the package, which contains the checksum to validate the data that is transferred between the networks. The Network Layer is employed by the routers to handle the network addresses.



Data link Layer
The data link layer takes input bits from layer one and arranges them into data structures called frames. It uses a frame header containing the sender and receiver addresses. These values do not remain constant and change while passing through the network nodes, routers or servers.


Physical Layer
The Physical Layer consists of the electrical part of the process of communication, the binary signals or bits that are transmitted and received in the process of exchange of data during the communication. The binary signal is a combination of 1's and 0's that may be repeated.

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OSI Model

1:17 PM kdhakal 1 comments
What is an OSI model?
 
      OSI stands for Open System Interconnect. It was developed by the International Organization for Standardization in 1974. The OSI model consists of seven layers with each layer having a different function of processing.
The seven layers of OSI Reference model are as follows:




OSI Model
OSI Model


What is web hosting? Find out here.


The Open System Interconnection model defines implementations for networking framework protocols in seven layers. Starting from the application layer in one station, the control is circulated from one layer to the other over the channel to the next station and back up the hierarchy.

Application layer

The application layer is the seventh or topmost layer of the OSI Model. The Application Layer is responsible for providing end-user services, such as file transfers, electronic messaging, e-mail, virtual terminal access, and network management. This is the layer with which the user interacts with the application. This interface may be command-line-based or GUI-based. Cisco routers and switches have a command-line interface, while a web browser uses a graphical interface.The application layer refers to applications that are network-aware. There are thousands of computer applications, but not all of these can transmit information across a network Examples of application layer programs are telnet, FTP, web browsers, and e-mail.



Presentation layer
The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the stack.


Session layer
 The session layer is the fifth layer of the OSI model that controls the connections between computers. Its responsibility is to establish, manage and terminate the connections between the client and remote applications. Session layer provides full duples, half duplex and simplex operaions of communication.

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Phases of web hosting

2:03 PM kdhakal 12 comments
There are four main phases or sequences of hosting a website, which are discussed below:

  • Simple internet presence
           This is the most common and most basic type of website that is simplest to set up and least expensive as well. This type of website is a medium of direct communication of an website owner to the clients. It contains general information about the business firm, its objectives, missions, news, press releases, products and views, services, contact information etc. It may contain annual reports and specialized news bulletins, as well as a dedicated area for visitor feedback.


  • Basic E-commerce or E-business website

               This category of website is somewhat complex version of the simple internet presence website, complex to mean that it consists of much more information compared to the simple internet presence websites. It consists of a number of substantial enrichment features that provide extra functionality to the website. The extra features may consist of an online store of various goods and services with secure ordering capabilities, integrated online call centers, FAQs and fact sheets, etc.


 Advanced E-commerce or E-business website 
     
                   Advanced websites consist of increased functionality such as web based software and core applications to dynamic IP based systems and applications. Off-the-shelf and custom software applications can be integrated with enterprise websites to enhance various processes in a number of areas such as automated processes, general business applications, data management functions and automated software, private IP-based networks, etc.


    • Fully Integrated E-business web presence
               At this fourth stage of development, the firm or enterprise has become a fully integrated E-business with intranets, extra-nets and discrete enterprise system working together. The back-office and front-office functions work together as an integrated system for the ease of ordering, asset and inventories management, and knowledge management throughout the system. In this model, the institution has become a true E-business.




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    Web hosting strategies

    1:02 PM kdhakal 2 comments
     Various web hosting companies have different kinds of offers for their clients, that differ in price and the offered service as well as the quality of the service. Some of the important points about web hosting strategies are discussed below.

    • The web hosts provide a place for storing the web pages so that they can be viewed online from anywhere.
    • The hosting company can be anywhere around the world.
    • There are two sectors of hosting companies like everything else - one that is cheap but with poor quality of service, and the other somewhat expensive but promising more prompt and quality service.
    • Cloud hosting is another important development step in web hosting that allows to share not only the web pages but also the programs that are too big to keep in personal computers.





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    File Hosting

    11:54 AM kdhakal 1 comments
    What is file hosting?
    A file hosting service is an internet hosting service, which is designed to host specially the static contents that comprise large files. Such files are generally allowed web and ftp access. Various file hosting companies have different rates for hosting the file according to the required file size, and the price is generally in terms of the required space.

    How to host a file?
    File hosting is carried out by hosting companies who offer the service free of charge or with a small amount of payment. In free hosting, there is usually some limitation over the number of files that can be hosted, or the maximum size of files hosted, while in paid hosting, there is almost no any limitation - the user can select any number of files of any size.

    Types of file hosting

    • Software file hosting
    • Personal file hosting
    • Content caching




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      Web Hosting

      2:47 PM kdhakal 3 comments
      What is web hosting?
      A web hosting service allows an individual and/or organization to make their websites accessible through the world wide web (WWW). The companies that provide the space on a server they own are known as web hosts, who provide the web hosting service. Web information is stored in documents called web pages, which are stored on computers called web servers; and the computers reading the web pages are called web clients.

      Hosting your web site on your own server is always an option. Following are some of the points that can be considered:

      Hardware
      Running a real website needs some powerful server hardware that cannot be replaced by a low cost PC. You'll also need a permanent source of power supply (so that the website is not down if there is load shedding or other power problem) and a permanent high-speed connection.

      Software
      Server-licenses usually have limits on number of users, and they are often higher than client-licenses.

      Labor
      Installing your own hardware and software cannot be accomplished with low labor expenses. Also bugs and viruses need to be dealt with, and the server needs to be running constantly in every situation.
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      Hybrid Topology

      12:29 PM kdhakal 0 comments
      A hybrid topology, as the name suggests, is an interconnection of two or more networks. The component networks may be ring, star, tree, mesh or any other, depending upon the requirement of a firm or institution. For example, in an institution, if there is a ring topology in one department, bus topology in the next department, star topology in another department and so on, all the departments can connect to each other through a bus topology that connects the ring, bus and star topologies of each department to each other. Such a topology that consists of more than one type of individual topologies is known as hybrid topology.



      Hybrid topology



      Advantages of hybrid topology

      • The benefits of several different types of topologies can be combined into one.


        Disadvantages of hybrid topology

        • Comparatively expensive than other topologies.

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          Mesh Topology

          11:20 AM kdhakal 0 comments
          A mesh topology is a computer network in which every node has a dedicated point-to-point connection to every other node in the network. A mesh topology has n*(n-1)/2 routes that connect 'n' devices in the network. Mesh topology work on the concept of routes. Message that is to be delivered to the destination can take any possible shortest and easiest routes that it can find.




          mesh topology
          Mesh Topology

          Advantages of Mesh topology

          • As it has multiple routes between the source and the destination, if one route fails, there would be a number of other routes through which data transfer can take place.
          • Traffic problem is minimized in this topology.
          • Troubleshooting is easier compared to other networks like star and ring.
          • Heavy load of data transfer has little impact on the performance of this topology.
          • This network can be easily expanded without affecting the existing users.

          Disadvantages of Mesh topology

          • It is expensive as it requires more cable than other topologies.
          • Installation is difficult and complicated.

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            Tree topology

            1:03 PM kdhakal 0 comments
            A tree topology consists of bus and star topologies framed in a common network. The tree like structure of this network allows the colleges, schools, universities and other institutions to maintain their own network as a branch of a bigger network through which they can maximize their area of access to the network. This type of network topology is most suitable for such networks which are widely spread and divided into many branches.
            On tree topology the hubs of each smaller topologies are connected to the central hub that controls the entire network. However, some nodes can be directly connected to the central hub.


            tree topology
            Tree topology



            Advantages of tree topology

            • It is possible to form a point to point connection with tree topology.
            • All the computers can access other computers which are in other larger and immediate networks.
            • Tree topology is best suited for branched out networks.

            Disadvantages of tree topology

            • In this topology, the length of the network depends on the type of cable utilized to form the network.
            • The entire tree topology would fail if the central trunk fails as it forms the backbone of the network.
            • The tree topology is comparatively more complex than the bus and star topologies. If it gets bigger, it would be difficult to configure and manage it.
            • It is expensive as more hubs and cables are required to install the network.


             
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            Ring Topology

            12:37 PM kdhakal 0 comments
            A ring topology consists of network of computers in which each node connects to exactly two other nodes.This forms a single continuous path for the flow of signals through each nodes of the network. Data travels from node to node, with each node along the way handling every packet. Each of the nodes in the ring topology are connected to each other through only one pathway, so the failure of only one link disrupts the whole network.
            To overcome this fallacy, the data in a ring topology is transmitted both clockwise and counter clockwise, so that if there is single break of the cable, all the nodes on both sides can be reached.




            Ring Topology
            Ring Topology




             Advantages of Ring Topology

            • It is an orderly network in which all the nodes in the network have equal access to all the resources.
            • Its performance is far better compared to star topology under heavy network.
            • It does not need network servers to manage the connections.
            Disadvantages of Ring Topology

            • If one of the workstations fails to operate, it may lead to the unusability of the whole network.
            • Addition and removal of devices in the network can affect the entire network.
            • Ring network is slower than  the Ethernet network.

             





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            Star Topology

            2:07 PM kdhakal 0 comments
            A star topology consists of a central connection hub to which devices are connected with UTP (Unshielded Twisted Pair) Ethernet. Contrary to the bus topology, a star topology utilizes a point-to-point connection to connect each node to the central hub. The hub acts as a signal booster as well, and all the data traffic that transverses the network passes through this hub.
            The entire network is dependent upon the central hub in a star topology, so if the entire network is not working, it means that there is problem in the hub. This makes it easy to troubleshoot the network because of the only one point for error correction. As all the computers in star topology are independent to each other and dependent only on the central hub, network failure or other network problems are less likely to happen. The privacy of each of the computers is also maintained in this topology.
            In star topology, new devices and nodes can be easily added and by just extending a cable from the hub.


            What is internet? Read here


            Advantages of star topology:
            • A star topology is simple in functionality and easy to manage.
            • If a problem occurs in the network, it can be easily isolated and cleared.
            • It is very easy to expand the star topology because of its simple format.

            Disadvantages of star topology:
            • The entire network of the star topology is completely dependent on the hub. If the hub fails, the whole network fails.
            • Network connection may slow down when the number of nodes increases or the cable lengthens.
            • Star topology needs more cable length than other topologies.
            • It is more expensive compared to bus topology.






            star topology
            Star Topology








            ZTE K3770-Z 3G USB Modem Datacard, 7.2Mbps, Fully Unlocked for Any 2G 3G Sim

            ZTE K3770-Z 3G USB Modem Datacard, 7.2Mbps, Fully Unlocked for Any 2G 3G Sim


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            Types of network topologies

            1:25 PM kdhakal 4 comments
            Bus topology

            A bus topology uses a single cable to connect all the devices used in the network. The single cable forms the backbone of the communication medium in which the devices are attached. To establish a communication, a signal originating from the source travels in both directions to all the machines connected on the bus cable until it finds the address of the device to which the data is to be delivered. If the destination device finds that the data is for its own address, then only it accepts the data. The topology consists of terminators at both ends so that the data does not continue bouncing to and fro.

            Advantages of bus topology:

            • If one of the station fails to operate, it does not affect the operation of other stations.
            • It can be a good replacement against other topologies.
            • It is very suitable for such networks which are more or less temporary and which are needed immediately.
            • It is easy to implement and extend.


            Disadvantages of bus topology: 

            • Data collision may occur when two or more nodes are transmitting the data at the same time.
            • It is not suitable if the traffic rates in the network is heavy.
            • It is very difficult to manage and troubleshoot a bus topology.
            • A fault in the cable may disable the whole network and it would be very difficult to find that fault.
            • Maintenance cost can increase unexpectedly at the long run.
            • Performance of the network is degraded when more computers are added to the network.



            Bus topology
            Bus topology
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            Network Topology

            4:42 PM kdhakal 1 comments
            A network topology refers to the interconnection of various nodes of a computer network. In other words, it defines the layout of the various devices that are part of the computer network.Topology is the virtual "shape" of the network, but it may not actually represent the actual physical design of the network that the various devices are connected to each other.
            There are two types of network topologies: physical and logical.

            A physical topology refers to the physical design of the computer network that includes the computers and other devices, their location and the various cables installed in the network.

            A logical topology means the mode of flow of data in the network in contrast to its physical arrangement.

            There are mainly six types of network topologies listed as under:
            • bus
            • star
            • ring
            • tree
            • mesh
            • hybrid
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            Types of computer networks (..... contd)

            3:28 PM kdhakal 0 comments
            MAN (Metropolitan Area Network)
            A MAN is a computer network that covers a geographical area that is larger than a LAN but smaller than a WAN,extending typically over a city. It is usually owned by a single entity like a government branch or a large organization.

            CAN ( Campus Area Network)
            A CAN is a computer network that spans multiple LANs but which is smaller than a MAN. It is mostly present in universities or a campus.

             SAN (Storage Area Network)
            This type of computer network is used to connect the servers to the data storage devices for storing the data or accessing the data that was stored previously on the device.

            VPN (Virtual Private Network)
            A VPN is a network of computers in which some of the links between the various nodes have open connections or have virtual circuits of some larger network, typically the internet, rather than joining them with physical wires. In other words, a VPN uses the connections of the internet or some other intranet to form a private network, without actual physical connection among the devices that form the node. This allows secure communications through the internet, because the VPN can be made accessible only by authorised personnels.

            PAN (Personal Area Network)
            A personal area network is a network of computers and/or other devices like PDAs (Personal Digital Assistant), cell phones, telephones, fax, printers, scanners etc. This network can be used to transfer files, emails, calender appointments, digital photos, music, etc. A PAN may be constructed through wire or wirelessly, and it typically covers an area of about 10 meters.
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            Types of computer networks

            3:14 PM kdhakal 0 comments
            On the basis of the area a network covers, it can be divided into the following types:

                *  LAN      -  Local Area Network
                *  WLAN  - Wireless Local Area Network
                *  MAN     - Metropolitan Area Network
                *  WAN     - Wide Area Network
                * SAN       -  Storage Area Network, System Area Network, Server Area Network, Small Area Network

                * CAN      - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
                * PAN      - Personal Area Network
                * DAN      - Desk Area Network


            The original categories of computer networks were only LAN, MAN and WAN. The other categories evolved during the advancements in the technology of computer networks.

            LAN (Local Area Network)

            A LAN is a network of computers and devices over a relatively short geographical area. An office building networked with computers,a school or college or a home usually contains a single LAN, though sometimes one building will contain a few small LANs (probably one per room), and occasionally a LAN will span a group of nearby buildings. In addition to operating in a limited space, LANs are also controlled by a single person or organization. A LAN also tend to use certain connectivity technologies, primarily Ethernet or Token Ring.

             WAN - Wide Area Network
            A WAN  spans a large physical distance compared to a LAN. The internet is the largest and the most common example of a WAN, that spans the whole Earth. A WAN can be considered as a collection of several LANs that are dispersed throughout the whole world. The network device Router connects several LANs to form the WAN. The Router also maintains both a LAN address and a WAN address in IP networking.

            WLAN  - Wireless Local Area Network
            WLAN is also a type of LAN(local area network) based on wireless network technology mostly referred as Wi-Fi. In contrast to a LAN, in WLAN no wires are used; radio signals are the medium for communication. To access any wireless network around, wireless network cards must be installed in the system. The wireless cards are connected to the Wireless Routers for the purpose of communication among the computers.




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            Computer Networks

            12:08 PM kdhakal 0 comments
            A computer network is a combination of computers and other computer related devices connected by communications channels for the purpose of sharing files and resources among the users. The network may be of many types, with unique features of its own.
            The primary objective of computer network is to share the files among various users. Among the various networks of computers, the internet is definitely the most important inventions of modern age. It is a huge source of information on any topic, it brought the era of emails and point to point communication through voice and video, allowing anyone to communicate with anyone else in the world; and it is also a great medium of new kind of business - the online business. Everyone in the world today depend so much on the computer networks and specially the internet, that it has become a part of our daily life.



            Computer Networks
            fig: Computer Networks
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            How to hack a website?

            10:19 AM kdhakal 1 comments


            Hacking a computer or a website are similar in terms of the security. The fundamental skill required for this purpose is programming, be it in any language. Learning a programming language is essential to learn the hacking procedures. It is easier to learn hacking if you have open source softwares like Unix. Along with the programming skills, some knowledge about the World Wide Web and HTML (Hyper Text Markup Language - the language of the web) is necessary. Good knowledge of English language is also a plus point. But only a lot of practice on programming and HTML will make one a successful hacker.


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            Hacking a computer

            11:58 AM kdhakal 0 comments
            Read about the generations of computers


            What is hacking?
            Some definitions of hacking:

            • A hacker is a person who breaks into computers, by gaining access to administrative controls.
            • In computing, a hacker is a person in one of several distinct (but not completely disjoint) communities and subcultures.
            • Unauthorized attempts to bypass the security mechanisms of an information system or network
            • hack - chop: cut with a hacking tool
            • hack - one who works hard at boring tasks
            • hack - be able to manage or manage successfully
            • hack - machine politician: a politician who belongs to a small clique that controls a political party for private rather than public ends
            • hack - cut away
            • hack - a mediocre and disdained writer
            • hack - kick on the arms
            • hack - a tool used for breaking up the surface of the soil
            • hack - cab: a car driven by a person whose job is to take passengers where they want to go in exchange for money
            • hack - fix a computer program piecemeal until it works
            • hack - an old or over-worked horse
            From all these definitions, it is clear that the word hacking has a wide range of meanings. But this word is famous as a person who breaks into computers, by gaining access to administrative controls, the first definition above.

            How to hack a computer?
            A typical way of hacking a computer that is part of a network is :
            • Network enumeration: Collect the required information about the target.
            • Vulnerability analysis: Concluding the various ways of attacking the target.
            • Exploitation: Attempting to attack the system by following the ways of attacking through the vulnerability analysis.
            In order to do so, there are several recurring tools of the trade and techniques used by computer criminals and security experts.


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