HTML and XHTML

        HTML (Hypertext Markup Language) is a special formatting language that programmers use to format document for display on the Web. You view a Web page written with HTML in a Web browser such as Internet Explorer, Safari, Firefox, Opera, or Google Chrome. Similarly, XHTML (extensible HTML) is a markup language that enables Web sites to be displayed more easily on microbrowsers in smart phones and other mobile devices, as well as on desktop and notebook computers.

Wi-Fi

      Computers and devices that have the appropriate wireless capability can communicate via radio waves with other computers or devices using  Wi-Fi (wireless fidelity), which identifies any network based on the 802.11 standards. Developed by IEEE,  802.11  is a series of  network standards that specifies how two wireless devices communicate over the air with each other. A designation of 802.11 a/b/g on a computer or device indicate it supports all three standards. The newest standard, 802.11n, uses multiple transmitters and receivers, known as MIMO (multiple-input multiple-output), to reach speeds from 2 to 10 times faster than 802.11g.

Mobile Computers and Mobile Devices

A mobile computer is a personal computer you can carry from  place to place. Similarly, a mobile device is a computing device small enough to hold in your hand.. the most popular type of mobile computer is the notebook computer. The following sections discuss the notebook computer and widely used mobile devices.

 Notebook Computers

notebook

         A notebook computer, also called a laptop computer, is a portable, personal computer designed to fit on your lap. Notebook computers are thin and lightweight, yet they can be as powerful as the average desktop computers usually are more expensive then desktop computers with equal capabilities.

On a typical notebook computer, the keyboard is on top of the system unit, and the monitor attaches to the system unit with hinges. These computers weigh on average from 2.5 to more 10 pounds (depending on configuration), which allows users to transport the computers can operate on batteries or a power supply or both.

UNIX and Linux

UNIX

         UNIX (pronounced YOU-nix) is a multitasking operating system developed in the early 1970s by scientists at Bell Laboratories. Bell Labs (a subsidiary of AT&T) was prohibited from actively promoting UNIX in the commercial marketplace because of federal regulations. Bell Labs instead licensed UNIX for a low fee to numerous college and universities, where UNIX obtained a wide following. UNIX was implemented on many different types of computers. After deregulation of telephone companies in the 1980s, UNIX was licensed to many hardware and software companies.

Computer viruses, worms, trojan horses, and rootkit

• ·         A computer virus is a potentially damaging computer program that affects, or infects, a computer negatively by altering the way the computer works without the user’s knowledge or permission. Once the virus infects the computer, it can spread throughout and may damage files and system software, including the operating system.

• ·         A worm is a program that copies itself repeatedly, for example in memory or on a network, using up resources and possibly shutting down the computer or network.

• ·         A Trojan horses (named after the Greek myth) is a program that hides within or looks like a legitimate program. A certain condition or action usually triggers the Trojan horse. Unlike a virus or worm, a Trojan horse doesn’t replicate itself to other computers.

• ·         A rootkit is a program that hides in a computer and allows someone from a remote location to take full control of the computer. Once the rootkit is installed, the rootkit author can execute programs, change settings, monitor activity, and access files on the remote computer. Although rootkits can have legitimates uses, such as in law enforcement, their use in nefarious and illegal activities is growing rapidly.