Windows 10 is better for playing video games than an operating system designed around video games
Valve is the company behind the Steam store and games such as "Portal," "Half-Life," "Left 4 Dead," and "Team Fortress." The company branched out into a dedicated gaming operating system in 2013, partnering with PC makers such as Alienware.
Ars Technica's test compared a custom-built PC running SteamOS and Windows 10 Pro. The PC has 8GB of RAM, an Intel dual-core "Haswell" CPU, and a 7,200rpm hard drive (over a faster solid state version). These are not the fastest specs but it is a level playing field.
The tests found that Windows 10 running on the machine was faster in every benchmark, whether the settings were turned all the way up or all the way down. The gap narrowed when the hardware requirements became less intense, but there was always a noticeable gap between the two.
One reason for the disparity could be down to the optimisation of games to the operating system. According to Ars commenter tipoo, Mac OS X has a similar issue. "I regularly see native Mac games lose 30-50% of the performance I would get under Boot Camp [the way to run Windows on a Mac as if it were the primary OS] on the same machine," they write.