Well, I personally think that SteamOS is the best what could happend to me as a gamer, as a developer, as a home office guy and someone who get tired of Microsoft usless additions and no fixes to known issues and of course as a linux fan. ( I use debian since 4 years on my local server and since ~3 years on my dedicated remote servers, actually this page is running on a debian 7 server
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With steam OS, there might be a reason for bigger devs to maintain their game on linux aswell.
Over the last two years we saw a trend. More games make it to linux / Mac Os.
Steam has it's own category for this. More and more games got a linux / Mac Os update aswell.
Now with steam os, a bridge between: hardware -- game developer -- game seller -- linux was made.
And this could lead to something big.
Some devs already see potentional in this and ported their games for steam os. ( Metro, Total War, ... )
Current benchmakrs show that windows has a slight advantege but steam os isn't done at all.
As you said, dual boot and the lack of support is a killer. But keep in mind that this isn't final at all and obviously valve will work with the companies to make something happen.
I think valve is pushing it faster forward now. They have the know how and contacts to many companies.
With steam os, we could have a faster and safer gaming experience. An os made for gaming.
Hopefully no Os cost at all. - No need to buy a os anymore.
No stupid performance popups which annoy you and throw you out of the game. ( well done MS )
I mainly use windows because I want to play. Of couse there are also some tools which I use which only works for windows, but if games are working on linux ( and run better ) than I could live with finding an alternative or try to get it running on linux aswell ( keyword wine )
( god I could write so much more, I try to keep it short now
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I'm excited about what will happen in the next few years. I belive linux gaming will get a higher role.
About your concers about steam machines:
Retailers need a license to build the steam machines. ( so they keep control of it )
But I hope it doesn't end like android, where every company is adding it's own additions to steam os and it's a clusterfuck then.
I agree a bit about your concerns with the different "tiers" of hardware.
Idk what their plan on this is.
But it's a good bridge between a console and a pc. - An upgradeable console technically.