Can you explain the evolution hierarchy of operating systems (Linux and Windows) from Unix?
Once upon a time operating systems were complex and unwieldy. One day in the late 1960s, Ken Thompson, Dennis Ritchie and a few of their colleagues at AT&T Bell Labs decided to write a simpler version of Multics to run games on their PDP-7, and thus Unix was born.
AT&T held the rights to the code, and licenses were expensive. Many other companies sublicensed Unix and sold their own version. Major players included DEC, HP, IBM, Sun. Unix variants added their own extensions, often nicking ideas from each other and from academia.
Meanwhile, in Berkeley, a number of academics were unhappy with the licensing situation and decided to create a version of Unix that didn't include any AT&T-licensed code. Thus in the early 1980s the Berkeley Software Distribution, or BSD, became a free variant of Unix. BSD first ran on Minicomputers such as PDP-11 and VAXen.
Meanwhile, on the East coast, Richard Stallman threw a fit when he couldn't get the source code to his printer driver. He founded the GNU (GNU's not Unix) project in 1983 intending to make a free Unix-like operating system, only better. After a little hesitation, the kernel of this operating system was chosen to be Hurd, which is going to be usable any decade now. Many components of the GNU project are included in all current free unices, in particular the compiler GCC.
Meanwhile, in Finland, Linus Torvalds went on a hacking binge in summer 1991. When he woke up, he realized that he'd written an operating system for his PC, and he decided to share it by putting it on an FTP server in a directory called linux. The success exceeded his expectations.
Many people created software distributions including the Linux kernel, many GNU programs, the X Window System, and other free software. These distributions (Slackware, Debian, Red Hat, SUSE, Gentoo, Ubuntu, etc.) are what people generally refer to when they say “Linux”. Most Linux distributions consist mostly of free-as-in-speech software, though software that is merely free-as-in-beer is often included when no free equivalent exists.
Other currently existing unices include the various forks of BSD (you get a choice of FreeBSD, NetBSD and OpenBSD, all being free, open and developed through the 'net), as well as a disminishing number of commercial variants targeted towards servers: and AIX, HP-UX, Solaris, and a few very minor contenders. Another proprietary unix-based operating system is Mac OS X running on Apple desktops, laptops and PDAs.
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Gilles explained very well the evolution from piece to another here, so I will cover the topic from more broad perspective and give some hints for further research.
From Bazaars and Research Labs to Closed Blobs and Market-marginalized Groups that I think are not that marginal at all
The key term to play with evolution is power. If you are dependent on an OS, for example in the form of security updates, you are dependent on the software-manufacturer and hence it has power over you. It can decide to stop publishing security updates or do any evil that its license allows it to do. If the OS is closed, the users must feel helpless because they cannot fix problems on their own, perhaps shown in hypocriticical feelings such as
I won't reinvent the damn wheel so please read about Bazaars, corporations and social-environmental-and-other problems below.
Ending, Now and Still Evolving
Culture, Money and Intellectual Capital
Wanna know more?
Your questions have too many confusions to attack them easily, such as presupposition about
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Renjith, there is no "root" operating system. History of operating systems is pretty long. I'd just recommend you to read next articles on Wikipedia:
Have fun, it's really interesting stuff...
For a really crazy diagram of the evolution of UNIX, see here. Not that it's very useful, though :).