what are SVN,GIT,mercurial etc?

i have a question and that is the title, from what i know they are something or someplace to store files over the internet so you can re开发者_开发问答trieve it from anywhere as long as you have internet, but why are there so many types of them? if all they do is the same thing that is to store files and then also allow you to retrieve them.

There not backup systems, they're version controls.

You can use Git or mercurial on your computer without any internet connection. There are two main ideas behind it :

• Track history of what you've done (finding what change introduced a bug, undo a crappy change...)
• Work in team : how to be sure that everybody has the newest version of a file without risking to overwrite your own changes

This is a really good introduction to Source Control:

http://www.ericsink.com/scm/source_control.html

Git and Mercurial are trying to meet the same requirements, but are Distributed Source Control systems. The basic ideas are very similar. Once you understand, read this:

http://hginit.com/

It's a Mercurial tutorial that will also teach you what distributed source control is all about.

http://en.wikipedia.org/wiki/Distributed_version_control_system — this will give you enough for initial understanding.

As answered in more detailed in other answers above; svn, git and mercurial are source control technologies. I.e. to keep files versioned. And optionally access via the internet. They are not designed specifically to share files over the internet.

Services specifically designed for internet based file sharing are DropBox, JungleDisk or even old fashioned FTP and sometimes illegal p2p such as BitTorrent.