Valve's Steam software has been around for well over a decade and has been changed quite a bit over the years. It always supported many platforms. There's a big change coming with for Steam, impacting users of older versions of Windows.

The newest features in Steam rely on an embedded version of Google Chrome, which no longer functions on older versions of Windows. In addition, future versions of Steam will require Windows feature and security updates only present in Windows 7 and above.

For the remainder of 2018 Steam will continue to run and to launch games on Windows XP and Windows Vista, but other functionality in Steam will be somewhat limited. For example, new features such as the new Steam Chat will not be available. We encourage all users on these operating systems to upgrade to newer versions of Windows in order to have ongoing access to the latest features of Steam, and to ensure future access to all games and other Steam content.

And there you have it, if you still have an XP or Vista gaming rig and use steam, you'd be advised to make a move and upgrade. It is noted that you'll still be able to launch games from your library in the meanwhile.