90. Linux

Linux is a freely available, open source, Unix-like operating system. Written originally for the PC by Linus Torvalds, with the help of many other developers across the internet, Linux now runs on multiple hardware platforms, from the smallest to the largest, and serves a wide variety of needs from servers to movie-making to running businesses to user desktops. Linux (often pronounced LIH-nuhks with a short "i") is a Unix-like operating system that was designed to provide personal computer users a free or very low-cost operating system comparable to traditional and usually more expensive UNIX systems. Linux has a reputation as a very efficient and fast-performing system. Linux's kernel (the central part of the operating system) was developed by Linus Torvalds at the University of Helsinki in Finland. To complete the operating system, Torvalds and other team members made use of system components developed by members of the Free Software Foundation for the GNU Project.

Linux also refers to the operating system. The kernel alone isn't enough to provide a functional computer system; it provides the foundation, and the operating system adds the tools to make the system usable. As an operating system, Linux consists of the kernel, plus an extensive set of libraries, compilers and debuggers, system utilities and programs, as well as one or more command shells. In other words, the operating system provides the tools for programming and for managing the system. Most of the tools were developed by the GNU project of the Free Software Foundation (FSF), and they provide enhanced versions of the traditional UNIX equivalents. Some others came from BSD Unix, developed originally at the University of California at Berkeley.

Most Linux distributions support dozens of programming languages. The most common collection of utilities for building both Linux applications and operating system programs is found within the GNU toolchain, which includes the GNU Compiler Collection (GCC) and the GNU build system. Amongst others, GCC provides compilers for Ada, C, C++, Java, and FORTRAN. The Linux kernel itself is written to be compiled with GCC. Proprietary compilers for Linux include the Intel C++ Compiler and IBM XL C/C++ Compiler. Most distributions also include support for Perl, Ruby, Python and other dynamic languages. Examples of languages that are less common, but still well-supported, are C# via the Mono project, sponsored by Novell, and Scheme. A number of Java Virtual Machines and development kits run on Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's J2SE RE, as well as many open-source projects like Kaffe.

As well as those designed for general purpose use on desktops and servers, distributions may be specialized for different purposes including: computer architecture support, embedded systems, stability, security, localization to a specific region or language, targeting of specific user groups, support for real-time applications, or commitment to a given desktop environment. Furthermore, some distributions deliberately include only free software. Currently, over three hundred distributions are actively developed, with about a dozen distributions being most popular for general-purpose use. Linux is a widely ported operating system kernel. The Linux kernel runs on the most diverse range of computer architectures: in the hand-held ARM-based iPAQ and the mainframe IBM System z9, in devices ranging from mobile phones to supercomputers. Specialized distributions exist for less mainstream architectures. The ELKS kernel fork can run on Intel 8086 or Intel 80286 16-bit microprocessors, while the µClinux kernel fork may run on systems without a memory management unit. The kernel also runs on architectures that were only ever intended to use a manufacturer-created operating system, such as Macintosh computers (with both PowerPC and Intel processors), PDAs, video game consoles, portable music players, and mobile phones.