Linux is a prominent example of free software and of open source development. Its underlying source code is available for anyone to use, modify, and redistribute freely, and in some instances the entire operating system consists of free/open source software.

Linux was originally developed for 32-bit x86-based PCs (386 or higher), today it also runs on (at least) the Compaq Alpha AXP, Sun SPARC and UltraSPARC, Motorola 68000, PowerPC, ARM, Hitachi SuperH, IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS, Renesas M32R, and Atmel AVR32 architectures; for many of these architectures in both 32- and 64-bit variants.

GNU
The Linux history is closely related to GNU. Plans for GNU were made in 1983 and in September of that year, the GNU project was publicly announced by Richard Mathew Stallman (The Founder and President of Free Software Foundation).

UNIX like OS
GNU was to be a complete Unix-like operating system composed entirely of free software. Software development work began in January 1984. By the beginning of the 1990s, the project had produced or collected most of the necessary components of this system, including libraries, compilers, text editors, and a UNIX shell. Thus the GNU mid-level portions of the operating system were almost complete. The upper level could be supplied by the X Window System (X Windows System or X11 is a networking and display protocol which provides windowing on bitmap displays with standard toolkit and protocol to build graphical user interfaces on Unix and Unix-like operating systems supporting by all other modern operating systems), but the lower level, which consisted of a kernel ( is a central component of operating system that responsible of the communication between hardware and software components), device drivers, and daemons, was still mostly lacking.

The Kernel of GNU
In 1990, the GNU project began developing the GNU Hurd (is a computer operating system kernel was distributed as free software under the GNU GPL) kernel, based on the Mach microkernel (is an operating system’s microkernel developed at Carnegie Mellon University to support the operating system research and project was remain in working from 1985 to 1994), but development proved unexpectedly difficult and proceeded slowly, and to date has only been marginally usable.

The Linux Kernel
Working on Linux Kernel was started by Linux Torvalds in 1991 while attending the University of Helsinki that was only a terminal emulation to access the University Servers at that time but later becomes the LINUX KERNEL. Torvals started that as a replacement of non-free Minix kernel. GNU’s free software and Linux kernel thus formed the basis of an operating system which has since been completed by the efforts of numerous members of free software and open source software communities. A number of free and open source software advocated, developers has been adopted the development process of Linux and now it is a complete desktop as well as a strong server based operating system.