According to Valve’s Greg Coomer, the beta is aimed at “intrepid Linux hackers” since the OS is not yet completed, for the non-technical user. As of now,
SteamOS Beta is an early, first-look public release of our Linux-based operating system. The base system draws from Debian 7, code named Debian Wheezy. Our work builds on top of the solid Debian core and optimizes it for a living room experience. Most of all, it is an open Linux platform that leaves you in full control. You can take charge of your system and install new software or content as you want.
SteamOS only supports Nvidia graphics cards right now, but AMD and Intel support is coming soon. For those wanting to build a Steam Machine of your own to run SteamOS, Valve has also released that information along with a plethora of other data. The current SteamOS beta installer is 960 MB and can be downloaded from Steam. Valve also announced SteamOS, Steam Machines and the Steam controller are expected to launch in 2014.