I accidentally put this under general. My bad, fixing that now. I assume something like this would go under help.
First off, I want to point out that this is not pirating or anything like that because you cannot have two different computers running steam under the same account at the same time and that steam already provides this kind of function if you use another computer, and you need to know someone who has the ALL the files. (If I am wrong about the same time statement and/or this is an inappropriate place for this thread, I apologize for my ignorance and please delete/move this post ASAP)
Secondly, I wanted to share this because I’ve done this before to free up space on my internal drive and to avoid having to slowly re-download 100+GB. I think everyone should know how to migrate their Steam installation.
(NOTE: This process is for a Windows installation. I do not have a Mac, so I do not know how to change the installation file path for a Mac. Someone else will have to write a tutorial on that step.)
My intentions clear, here we go.
Note: If you are migrating to a different computer, run the steam installation there first. Otherwise skip Step 2 and 3.
Step 1: Copy your steam folder to wherever you want to play from. (See Note on Step 1 if you want to only copy certain things)
Step 2: Export the registry key “HKEY_LOCAL_MACHINE\SOFTWARE\Valve” to a .reg file IF you are migrating to a different computer. (how to do this beyond the scope of this tutorial, but easily done)
Step 3: Merge the .reg file on the new computer.
Step 4: In your registry, under “HKEY_LOCAL_MACHINE\SOFTWARE\Valve\Steam”, modify BOTH the install path and service install path to the new path.
You have now migrated your steam installation!
Note on Step 1: If you only want to copy certain games, follow this steps:
Step 1.1A: If have Source engine games you want to copy, you must copy all the .gcf files that have source in their name and all .gcf files that have the name of the game in the file name and a few more .gcf files (I am not sure on the dependencies of these “few more,” but I can tell that this is the way it works). You then must also copy the games you want that are under \steamapps[username].
Step 1.1B: For non-Source games, copy all the .ncf files, all the files under \steamapps\common[game name], all the files under \userdata[your account number][the app number] (app number for garry’s mod is 4000), and (preferably) the entire steam\games folder.
You now know how to move steam around (and take it with you!)
To run your steam games (instantly) on any computer with steam, simply use the registry file and edit it as necessary.
With this setup, you can also have multiple installations of steam, on separate drives, on separate computers, so if you go to your friend’s house, you don’t have to mess with their installation. Just export their registry file before using yours so they can restore their setup, and when your done, simply delete “HKEY_LOCAL_MACHINE\SOFTWARE\Valve” and restore the old one.
EDIT: I feel silly now. An easier way (no fooling with registry) to do this has already been posted here->https://support.steampowered.com/kb_article.php?ref=7418-YUBN-8129
But now you know some of the file structure and how to do it manually (in case of backup or etc)