Adoption of Windows 8.1 saw a notable jump among Steam users during December 2013, according to Valve's most recent monthly hardware survey.
The 64-bit version of Windows 7 remains the operating system that the majority of Steam users run, although just barely: The proportion dropped by 1 percentage point to 50.76 percent. The decrease in Windows 7 and 8 usage can likely be attributed to Windows users upgrading to Windows 8.1 — 8.53 percent of Steam users are now running the 64-bit version of Microsoft's latest operating system, a 2.42 percent increase over the November numbers. Microsoft released Windows 8.1 as a free download at the end of October.
Meanwhile, Linux usage was back up in December to 1.07 percent after a drop during November from 1.06 percent to 0.98 percent (not counting Linux distributions that may fall under Valve's "other" category). Mac usage stayed relatively flat, going from 3.48 percent to 3.68 percent.
2013 saw a significant push from developers to bring their games to Linux, spurred on by Valve's investment in the platform through SteamOS and Steam Machines. But for now, Windows is still king on Steam, with more than a 94 percent share of the user base.