I am going to share a somthing I figured out by reading some batch programming.
It takes a little work, but once done, you will never have to do it again. Now, you can have all your PC games on an USB flash drive, cd or external HDD and play them from there without having to install them again.
Lets say you have two HDD's in your PC, the primary HDD is for windows installation and the secondary HDD is for games and program installments. Lets say your primary HDD fails and you have to buy a new one with a new windows installed on it,the problem is, most of your games on the other HDD wont work now, because they are missing essential .DLL (dynamic link library) files.
Lets say you have a game called Unreal installed in the path d:\Unreal and the .exe file is called unreal.exe, and you start the game double clicking unreal.exe.
It will give an error message about a missing .dll file, and in this example lets call the file it needs unreal3d3.dll, download this file.
In c:\Unreal you have to make a folder, you can call the folder whatever you want, I call my folder u-portable so it should look like this: c:\unreal\u-portable
Copy the unreal3d3.dll to the u-portable folder you just made in your c:\unreal, here comes the trick, open a new text document and type this in it:
Save the text document in c:\unreal, you can call what you want. Remember to save it as all file types, and give it the extension .bat
Like this: unreal-portable.bat
Now you can copy your game to any HDD , flash-Drive, or cd and play it from there, without having to install it again.
I, for example, play League of Legends from a flash-drive.