Xi3, one of several companies approached by Valve to work on a "Steam Box" console — though Valve now disavows involvement — has opened pre-orders for its gaming-optimized PC. The Piston, which was first shown off at CES in January, uses a small enclosure like that of Xi3's other modular computers. The $999.99 price tag gets you a 128GB SSD, a 3.2GHz quad-core AMD R464 processor with integrated graphics, and 8GB of RAM, with more details forthcoming; we've previously heard that it will be optimized to work with Steam and Big Picture Mode. Pre-order customers can upgrade the size of the SSD to 256GB or 512GB, but the latter almost doubles the price of the machine, adding $750. Further details will be forthcoming as the Piston nears release around the end of 2013.

The Piston isn't priced to compete with the upcoming generation of PlayStation and Xbox, and what we've heard of its specs indicates it won't match top-tier gaming PCs, but Xi3 says it combines the small form factor of consoles with the "upgradeability of computer gaming rigs." The company is also offering a deal for early adopters: until March 17th, the Piston is being sold for $100 off its list price. While the Piston is the first Steam Box we've seen so far, it could eventually be one of many, based on both Windows and Linux and sold at a variety of price points. According to previous descriptions of the line, the Piston fits firmly into the most expensive "Best" category, compared to "Better" machines that will sell for around the price of a console and super-cheap "Good" ones meant for casual games or streaming.

Update: Valve's Doug Lombardi has clarified to Eurogamer that the company no longer has any association with Xi3, despite an announcement of funding made at CES earlier this year.

Update 2: Xi3 tells Kotaku that "we were asked to build a product specifically for Valve," and disputes the lack of a relationship between the companies. "Just because Valve may not ‘currently' have any ‘involvement with any product of (ours)' doesn't mean that such involvement won't exist in the future," said a representative.