Q:

Where do files of one branch go when I checkout to another branch?

I have a git repository at G:\C\BIT. It has two branches dev and master. master is empty and dev has three follders A, B, and C. Now when I am in dev branch then these folders show in computer. But when I checkout to master branch all the three folders A, B and C become invisible. Not only they are invisible but they don't take space on my hardisk too. G:\C\BIT in dev is 4 MB and in master 2.75 MB. My question is 

Where do files of one branch go when I checkout to another branch? Are they hard deleted and then redownloaded when I checkout to the former branch again?

A:

Your git repository is stored in the .git directory of your working directory.  When you check out a new branch, files may be added or deleted from your working directory, but they remain untouched in the git repository.
Git only operates on local files; while it has facilities for synchronization changes to and from remote repositories, actions like checking out a file or committing changes only affect the local repository.

