Valve has explained the reason many Steam users are experiencing DirectX installs whenever a new or older game is downloaded onto the users system.
According to Valve software engineer John McCaskey, the issue is with Microsoft in how it packages software, which in some cases has multiple D3DX instances showing up in their .NET configuration files.
“This is not a matter of making sure your overall DirectX install being up-to-date,” said McCaskey on the official Steam forums. “Microsoft has a helper library with D3D called D3DX. You'll find binaries for this like d3dx9_43.dll in your Windows\system32 folder. There are over 40 different versions of the D3DX library for D3D9 alone, and many more for D3D10 and 11 as well. Each game that uses the D3DX helper library is linked to a specific version. As such the game must run the correct D3D installer version that it was specifically compiled with to ensure the binaries exist. Even if a later version of the binary is already installed, that version cannot be used, and even if your DirectX install is up-to-date because you've run a more recent version of the installer that is not guaranteed to have installed all previous versions.”
McCaskey said that even if a version is installed for x86 it doesn't guarantee the same version is installed for x64, therefore, 64 bit and 32 bit games could run the same installer version but target different platforms.
“Furthermore, Microsoft's licensing terms prevent anyone from distributing the files directly, the only way to distribute them is to run the installer, that's also the only supported method from Microsoft to check that the correct version installed,” McCaskey explained. “Trying to manually check for the correct versions is extremely complicated because there are numerous files that must all be present and individual system configuration options like dll search paths complicate the situation.
"Games which don't use the D3DX helpers (such as Source engine games) don't require running the annoying installer on first launch as they only depend on major D3D9/10/11 versions being installed. However, games that do use D3DX must run it as it's the only way Microsoft has allowed for distributing and checking the version info on the files
"We can't stop. It's required due to a bad versioning/packaging scheme as well as bad redistribution licensing terms on the D3DX libraries."
McCaskey said it could be made a bit better on the Steam side of things, but in order for that to happen, game manufacturers would have to change the way games are packaged for the service.
"The one thing that could be made better on our side is that Steam could be smart enough to know if an exactly matching version of the DX installer is already downloaded and share that content so you don't download it with each game," he said.
"Since the installer is relatively small compared to most game installs that wouldn't be a huge win, though, and requires a good deal of new complexity for partners in how they package up their games and manage installation dependencies.
"You'd also still end up with lots of different versions of the installer, since as discussed above they are often targeting different D3DX versions and as such are all required. As such any improvement to avoid duplicates isn't an immediate priority, but we may be able to improve it slightly in the future."