FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX.  Although for legal reasons FreeBSD cannot be called “UNIX”,^[1] as the direct descendant of BSD UNIX (many of whose original developers became FreeBSD developers), FreeBSD’s internals and system APIs are UNIX-compliant. Thanks to its permissive licensing terms, much of FreeBSD’s code base has become an integral part of other operating systems such as Mac OS X that have subsequently been certified as UNIX-compliant and have formally received UNIX branding.^[2]  With the exception of the proprietary Mac OS X, FreeBSD is the most widely used BSD-derived operating system in terms of number of installed computers, and is the most widely used freely licensed, open-source BSD distribution, accounting for more than three quarters of all installed systems running free, open-source BSD derivatives.^[3]

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Unix

Unix (officially trademarked as UNIX, sometimes also written as Unix) is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna. The Unix operating system was first developed in assembly language, but by 1973 had been almost entirely recoded in C, greatly facilitating its further development and porting to other hardware. Today's Unix system evolution is split into various branches, developed over time by AT&T as well as various commercial vendors, universities (such as University of California, Berkeley's BSD), and non-profit organizations.

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Linux

Linux ( /ˈlɪnəks/ lin-əks,^[5][6] also pronounced /ˈlɪnʊks/ lin-uuks^[7][8][9]) is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds.^[10][11] Linux system distributions may vary in many details of system operation, configuration, and software package selections.

Linux runs on a wide variety of computer hardware, including mobile phones, tablet computers, network routers, televisions^[12][13], video game consoles, desktop computers, mainframes and supercomputers.^{[14][15][16][17]} Linux is a leading server operating system, and runs the 10 fastest supercomputers in the world.^[18] In addition, more than 90% of today's supercomputers run some variant of Linux.^[19]

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