Linux is a computer operating system and its kernel. more...
It is one of the most prominent examples of free software and of open-source development: unlike proprietary operating systems such as Windows and Mac OS, all of its underlying source code is available to the public and anyone can freely use, modify, and redistribute it.
In the narrowest sense, the term Linux refers to the Linux kernel, but it is commonly used to describe entire Unix-like operating systems (also known as GNU/Linux) that are based on the Linux kernel combined with libraries and tools from the GNU Project and other sources. Most broadly, a Linux distribution bundles large quantities of application software with the core system, and provides more user-friendly installation and upgrades.
Initially, Linux was primarily developed and used by individual enthusiasts. Since then, Linux has gained the support of major corporations such as IBM, Sun Microsystems, Hewlett-Packard, and Novell for use in servers and is gaining popularity in the desktop market. Proponents and analysts attribute this success to its vendor independence (the opposite of vendor lock-in), low cost, security, and reliability.
Linux was originally developed for Intel 386 microprocessors and now supports all popular computer architectures (and several obscure ones). It is deployed in applications ranging from embedded systems (such as mobile phones and personal video recorders) to personal computers to supercomputers.
In 1983, Richard Stallman founded the GNU project, which today provides an essential part of most Linux systems (see also GNU/Linux, below). The goal of GNU was to develop a complete Unix-like operating system composed entirely of free software. By the beginning of the 1990s, GNU had produced or collected nearly all of the necessary components of this system—libraries, compilers, text editors, a Unix-like shell, and other software—except for the lowest level, the kernel. The GNU project began developing their own kernel, the Hurd, in 1990 (after an abandoned attempt called Trix). According to Thomas Bushnell, the initial Hurd architect, their early plan was to adapt the BSD 4.4-Lite kernel and, in hindsight, "It is now perfectly obvious to me that this would have succeeded splendidly and the world would be a very different place today" . However, due to a lack of cooperation from the Berkeley programmers, Stallman decided instead to use the Mach microkernel, which subsequently proved unexpectedly difficult, and the Hurd's development proceeded slowly.
Meanwhile, in 1991, another kernel—eventually dubbed "Linux"—was begun as a hobby by Finnish university student Linus Torvalds while attending the University of Helsinki. Torvalds originally used Minix, a simplified Unix-like system written by Andrew Tanenbaum for teaching operating system design. However, Tanenbaum did not permit others to extend his operating system, leading Torvalds to develop a replacement for Minix. Linux started out as a terminal emulator written in IA-32 assembler and C, which was compiled into binary form and booted from a floppy disk so that it would run outside of any operating system. The terminal emulator was running two threads: one for sending and one for receiving characters from the serial port. When Linus needed to read and write files to disk, this task-switching terminal emulator was extended with an entire filesystem handler. After that, it gradually evolved into an entire operating system kernel intended as a foundation for POSIX-compliant systems. The first version of the Linux kernel (0.01) was released to the Internet on September 17, 1991, with the second version following shortly thereafter in October . Since then, thousands of developers from around the world have participated in the project. Eric S. Raymond's essay The Cathedral and the Bazaar discusses the development model of the Linux kernel and similar software.
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