Valve’s Steam Machines are finally available to buy in certain countries, but the results from one early performance test aren't exactly positive.

Ars Technica used a dual-boot SteamOS/Windows machine in its tests, and according to the site, benchmarking tool Geekbench 3 showed “a definite edge for Windows 10, especially in terms of floating point operations” when it came to CPU performance. Click here for the full results.

Ars then tested each operating system by playing Middle-Earth: Shadow of Mordor and Metro: Last Light Redux, and the gap between the two was even more marked.

“No matter how you slice it, running these two high-end titles on SteamOS comes with a sizable frame rate hit; we got anywhere from 21- to 58-percent fewer frames per second, depending on the graphical settings,” wrote Ars Technica’s Kyle Orland.

“On our hardware running Shadow of Mordor at Ultra settings and HD resolution, the OS change alone was the difference between a playable 34.5 fps average on Windows and a stuttering 14.6 fps mess on SteamOS.”

Valve's own Source engine games didn’t fare any better, either.

“Portal, Team Fortress 2, and DOTA 2 all took massive frame rate dips on SteamOS compared to their Windows counterparts; only Left 4 Dead 2 showed comparable performance between the two operating systems (though there's no sign of those SteamOS frame rate improvements Valve cited years ago),” said Orland.

However, it’s worth noting that the PC used in the tests was two years old so newer hardware might be better suited to take advantage of high-end OpenGL features. It’s also worth noting that games built from the ground up with OpenGL and Linux in mind might fare better too.

There’s also updates coming from both sides: Microsoft is releasing DirectX 12, while OpenGL is releasing Vulkan.

And of course, this is just one test across a handful of games.

Even so, it isn’t the most encouraging result, especially from an OS with vastly fewer games available for it than Windows 10.

“Hopefully, Valve and other Linux developers can continue improving SteamOS performance to the point where high-end games can be expected to at least run comparably between Linux and Windows,” wrote Orland.

“Until then, though, it's hard to recommend a SteamOS box to anyone who wants to get the best graphical performance out of their PC hardware.”