Steam – How does Steam decide when to update the games

I know of only one way that this can happen in windows, and has nothing to do with Steam other than their not-so-great decision to install all content into Program Files.

If you are on Windows 7 or Windows Vista, and you have UAC set to ON, then change it later to OFF, this can happen.

UAC does thing evil thing where if a program tries to write to a "protected" area like Program Files, EVEN IF YOU ARE ADMINISTRATOR, when you get a UAC prompt and give permission, it actually writes any files that would normally go into that directory into a "virtualized" directory somewhere else.

If you turn off UAC, that will no longer happen, and as an awesome bonus, it will no longer know about the files that it virtualized.

So in your case, if you had UAC on, installed a ton of games, then later got sick of UAC and turned it off, this would happen as you described.

See the second paragraph in "Features" in the article on User Account Control.

If you have done this and turn on UAC again, your content will come back, but be a TOTAL mess because if you've downloaded more stuff with UAC off, then that will be invisible when you turn UAC on, and vice versa.

this drove me a little crazy once before I realized what was happening.

i'm curious to know if this is your issue.

A lot of the files, such as assets (images, textures, models), config files etc, are shared between Windows & Mac - They are the same files and can be used on both Windows and Mac without problems as proved here:

Do Mac and Windows versions of Source games contain the exact same files?.

However, the actual executables (.exe for Windows, .app for Mac) and library files .dll for Windows, .a for Mac) differ greatly (and are written differently, so you can't just change the extension and hope for the best).

Assuming Steam doesn't remove the Windows executables when you verify game cache on the Mac side (as SevenSidedDie fears), then theoretically you could get away with installing Steam (just Steam!) on the Mac side of things, and creating symbolic links to the files and folders that you need.

You will need to create symbolic links to

• The Game's directory in the steamapps folder
• Any Source .GCF files in the main directory (I can't remember what they're called off the top of my head, I will have a look when I get home, otherwise feel free to edit them in!)

Here is an answer I posted about creating symbolic links in Windows: Team Fortress 2 won't install on custom location.

Just remember to create Directory links for entire directories, and File links for individual files.

Edit:
Thanks to SevenSidedDie, I now know how to create symbolic links on a Mac! :) The command is:

ln -si <real file/folder path> <link name>

As pointed out, some programs wont follow symbolic links, but I've never had a problem doing this for Steam on Windows.