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Internet

Internet

The Internet, sometimes called simply "the Net," is a worldwide system of computer networks - a network of networks in which users at any one computer can, if they have permission, get information from any other computer (and sometimes talk directly to users at other computers).
History of the Internet
Four purposes (military – cold war and educational – universities, scientific and commercial), four fundamental concepts for the foundation of the Internet (ARPANET, RAND,NPL, Cyclades). They started with packet switching, set of internet communication protocols (TCP/IP),  distributed and decentralized network (packets can be routed or rerouted in more than one direction)
Basic concepts
Today, the Internet is a public, cooperative, and self-sustaining facility accessible to hundreds of millions of people worldwide. Physically, the Internet uses a portion of the total resources of the currently existing public telecommunication networks. Technically, what distinguishes the Internet is its use of a set of protocols called TCP/IP (for Transmission Control Protocol/Internet Protocol). Two recent adaptations of Internet technology, the intranet and the extranet, also make use of the TCP/IP protocol.
The Internet means computer networks connected together by so called network nodes (uzle). The node may be a computer, or another device (eg. router). They determine the next network point to which a packet should be forwarded toward its destination.
Each computer connected to the internet has its IP address. An Internet Protocol (IP) address is a numerical label that is assigned to devices participating in a computer network using the Internet Protocol for communication between its nodes. An IP address serves two principal functions in networking identification and location addressing.
IP address as a 32-bit number and this system, known as Internet Protocol Version 4 or IPv4, is still in use today. However, due to the enormous growth of the Internet a new addressing system (IPv6), using 128 bits for the address, was developed in 1995 and standardized in 1998. Although IP addresses are stored as binary numbers, they are usually displayed in human-readable notations, such as 208.77.188.166 (for IPv4), and 2001:db8:0:1234:0:567:1:1 (for IPv6). The following three blocks of the IP address are reserved for private internets (local networks): 10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.31.255.255, 192.168.0.0 - 192.168.255.255 and 169.254.0.0 -169.254.255.255.
To make remembering easier domain names are used instead of IP addresses. The domain name service (DNS) converts domain names to IP addresses:
 e.g.: www.google.com  74.125.87.103
Internet services:
For many Internet users, electronic mail (e-mail) has practically replaced the Postal Service for short written transactions. Electronic mail is the most widely used application on the Net. You can also carry on live "conversations" with other computer users, using Internet Relay Chat (IRC), Instant Messaging, Voice over Internet Protocol. More recently, Internet telephony hardware and software allows real-time voice conversations.
Social networking websites have recently became very popular.
The most widely used part of the Internet is the World Wide Web (often abbreviated "WWW" or called "the Web"). Its outstanding feature is hypertext, a method of instant cross-referencing. In most Web sites, certain words or phrases appear in text of a different colour than the rest; often this text is also underlined. When you select one of these words or phrases, you will be transferred to the site or page that is relevant to this word or phrase. Sometimes there are buttons, images, or portions of images that are "clickable." If you move the pointer over a spot on a Web site and the pointer changes into a hand, this indicates that you can click and be transferred to another site.
Using the Web, you have access to millions of pages of information. Web browsing is done with a Web browser The appearance of a particular Web site may vary slightly depending on the browser you use.
E-commerce is used by all types of businesses to sell all types of products. E – banking is convenient and flexible for the customers who do not have time to go to the bank to perform transaction. E- learning is cost effective for both students and institutions.
Web Browsers:
Web Browsers are applications which enable users to view individual web pages, or collection of linked web pages, that comprise websites. Commonly used browsers are Internet Explorer, FireFox, Opera ...
Search Engines:
Search Engines are websites that help users to find other websites using a searchable database. Different search engines use different approaches (technologies) and it may be possible to find information using one search engine that you will not find using another.
Almost all modern search engines use programs called spiders and automated crawlers to visit as many websites as possible, and catalogue their contents to produce searchable index. The user enters a search term (key word) and activates search algorithms which with the help of the index return results. (www.google.com, www.yahoo.com, www.seznam.cz.....)
There are also meta-search engines that send users request to several other search engines and/or databases and aggregates the results into a single list or displays them according to their source. (www.dogpile.com, www.ixquick.com ....)
Cookies are small files, which are sent by the website you visit and your browser places them on your hard disk. These files may contain your personal data.
Security
1.       Protected websites – websites which require username and password
2.       Secure websites – (banking, websites where you enter your credit card number...) – padlock item, https – these sites use enctryption when transferring information
3.       Digital certificates – the equivalent of a driver's license, a marriage license, or any other form of identity. The only difference is that a digital certificate is used in conjunction with a public key encryption system. Digital certificates are electronic files that simply work as an online passport. Digital certificates are issued by a third party known as a Certification Authority such as VeriSign or Thawte. These third party certificate authorities have the responsibility to confirm the identity of the certificate holder as well as provide assurance to the website visitors that the website is one that is trustworthy and capable of serving them in a trustworthy manner.[1]
4.       Antivirus software
5.       Firewalls – can exist in hardware and in software – acts as a barrier
6.       Be aware of the risks of using the internet
Digital certificate. Načteno z Topbits: http://www.topbits.com/digital-certificates.html