In computer science, object-oriented programming language introduced in 1995 by Sun Microsystems, Inc. Java facilitates the distribution of both data and small application programs, called applets, over the Internet, aided by its object-oriented programming style. Java applications do not interact directly with a computer’s central processing unit (CPU) or operating system and are therefore platform independent, meaning that they can run on any type of personal computer, workstation, or mainframe computer. This cross-platform capability, referred to as “write once, run everywhere�, has caught the attention of many software developers and users. With Java, software developers can write applications that will run on otherwise incompatible operating systems such as Windows, the Apple Computer operating system, OS/2, or UNIX. To use a Java applet via the World Wide Web (WWW or Web)—the system of software and protocols that allows multimedia documents to be viewed on the Internet—a user must have a Java-compatible browser, such as Netscape Navigator from Netscape Communications Corporation, Internet Explorer from Microsoft Corporation, or Hot Java from Sun Microsystems. A browser is a software program that allows the user to view text, photographs, graphics, illustrations, and animations on the Web. Java applets achieve platform independence through the use of a virtual machine, a special program within the browser software that interprets the byte code, the code that the applet is written in, for the computer’s CPU. The virtual machine is able to translate the platform-independent byte code into the platform-dependent machine code that a specific computer’s CPU understands. Applications written in Java are usually embedded in Web pages, or documents, and can be run by clicking on them with a mouse. When an applet is run from a Web page, a copy of the application program is sent to the user’s computer over the Internet and stored in the computer’s main memory. The advantage of this method is that once an applet has been downloaded, it can be interacted with in real time by the user. This is in contrast to other programming languages used to write Web documents and interactive programs, in which the document or program is run from the server computer. The problem with running software from a server is that it generally cannot be run in real time owing to limitations in network or modem bandwidth (the amount of data that can be transmitted in a certain amount of time). Java therefore enables a far greater degree of integration between computers over the Internet than hitherto possible, as well as new patterns of software distribution and use, with downloaded applets replacing large application programs. Java grew out of a research project at Sun Microsystems in the early 1990s that focused on controlling different consumer electronics devices using the same software. The original version of Java, called Oak, needed to be simple enough to function with the modest microprocessors found in such consumer devices. Following the introduction by the National Center for Supercomputing Applications (NCSA) of the Mosaic browser in 1993, Oak was recast by Sun Microsystems developers. In 1994 Sun Microsystems released a Java-compatible Internet browser, called HotJava, that was designed to read and execute Java applets on the Web. Sun Microsystems licensed Java to Netscape Communications in November 1995, and its Navigator browser supports Java applications. Microsoft also licensed Java, in 1996, for its Internet Explorer browser. Microsoft developed a programming language, called Visual J++, to integrate Java, through its ActiveX technology, with its browser. Visual J++ is optimized for the Windows operating system. (Sun has frequently complained that Microsoft’s policies towards Java have been an attempt to dilute its cross-platform capabilities, and in October 1997 filed a complaint with a California court alleging that the version of Java shipped with Microsoft’s latest browser, Internet Explorer 4.0, was incompatible with other versions.) Various other Web browsers are also capable of supporting Java applications and applets. JavaSoft, a division of Sun Microsystems with responsibility for Java and its business development, has created JavaOS, a compact operating system for use on its own JavaStation network computers, as well as in cellular telephones, pagers, Personal Digital Assistants (PDAs), and other devices. Microsoft ® Encarta ® Premium Suite 2005. © 1993-2004 Microsoft Corporation. All rights reserved.

Unlike the Microsoft Windows operating system, for example, Linux is available from many different companies each adding their own features, such as a graphical installation routine, but all relying on a basic set of operating system functions. The software that constitutes the Linux operating system is of two main parts. There is low-level software, known as the Linux kernel, that manages your computer hardware and the many programs that are running at any given time, and there is the Linux Operating System, which is the collection of utility programs that allows you to copy files, delete files, and do all of the other actions that make a computer so useful. The first version of Linux was written by a second-year student of computer science at the University of Helsinki in Finland, Linus Torvalds, and was released in 1991. Since then, Linux has been refined and developed to become one of the most popular operating systems in the world. It is widely used in the business community to support office and commercial systems as well as being an increasingly popular operating system for personal computing. In many respects, Linux is an operating system, just like many others, and thus of little interest to all but a relatively small group of software developers. What makes Linux both interesting and different is the way in which it has evolved. Rather than being developed as a commercial product, the original version of Linux was released to a public Internet forum and was subsequently adopted by software engineers worldwide as a programming challenge. With literally thousands of minds focused on Linux, it rapidly became a fast, reliable and ubiquitous operating system. One further feature that endeared it to so many people was that, with virtually all of the hard work done by people who volunteered their efforts, the basic Linux operating system is free. Linux was continually enhanced through the 1990s, with thousands of enthusiast programmers working to develop applications for it. In addition to this distributed development mechanism, commonly known as “open source�, software, several commercial enterprises have released their own Linux-based products. A number of vendors have gathered together various pieces of software and presented them in a distributable format that makes Linux look like any operating system with which people are familiar. The Linux releases from these companies are called distributions. The Red Hat distribution is the most popular commercial offering with Caldera, Debian, and Suse some of the other leading names. The way in which Linux has been developed makes it important in the advancement of computing across the world. Because it can be scaled to run in almost any computer with very few resources, it has become a natural choice for low-budget computer users. Old computers that have become a part of history in the developed world can be put to good use in developing countries as Linux enables the full potential of these computers to be exploited. In the countries of Asia, Africa, and Latin America, Linux has appeared as a solution for the masses of computer enthusiasts. Microsoft ® Encarta ® Premium Suite 2005. © 1993-2004 Microsoft Corporation. All rights reserved.