Linux
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There are many many many flavors of linux. I recommend you Ubuntu (
http://www.ubuntu.com/desktop/take-the-tour); but if you want something more lightweight use Xubuntu (
http://xubuntu.org/screenshots/). I know ubuntu looks prettier than xubuntu but that comes with a price. If you have something better than a dual core like i3/i5/i7 then you shouldn't have any speed issues with Ubuntu. Call me if you're confused.
In step 3, if you want to install xubuntu, choose xubuntu from the drop down menu instead of ubuntu.
If you have space, allocate about 15 - 30GB if not atleast (8GB). More the better. The operating system requires about 4 GB so all the additional GB's are for your files.
Things to remember
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When that video says you dont need an antivirus, it means that when you're booting your machine in linux (NOT when you're using windows. You still need an antivirus in windows)
Programs from windows will NOT run in linux. In case of codes, you'll have to recompile them again in linux to make them work.
You will NOT be able to access the space allocated for linux from windows.
Yes, most servers use some form of *nix (abbreviation to include all unix/linux based OS).
Call me if you have any questions.
Regards,
Ayush