Linux (Unix) is a lean, mean and technically simple (that means mostly to the technical whizzes are the one who like it) multi tasking, multi user operating system that is particularly good with communications (it was developed by 2 techno-wizards at Bell labs)
Windows is a clumsy, dos shell, unreliable and system greedy operating system. Kept "efficient" by endless updates.
Unfortunately unix/linux/xenix somehow became the realm of the tekkies and Big Brother Bill (clever boy that) saw the commercial (read profit!) opportunities in operating systems, couldn't get his hands on the good one (because the tekkies saw the big bad wolf in businessman's clothing) so put his money (lots and lots and lots) into the "bad" system and we all live happily ever after!!
New versions of Unix/Linux like redhat are excellent and run well with windows lookalike interfaces/routines.
You can even (O Lord!!) run windows and Linux on the same machine (for gamers). For Linux .you can get cheap open-source software packages that are microsoft compatible - wordprocessors, spreadsheets powerpoint .etc
One big point about Unix - there are almost NO viruses (thus far) written for the packages that run on it so it is a very safe system to use on the internet.