Valve has unveiled the physical design of its prototype Steam Machine, and it looks vaguely like a black Xbox 360.

The Verge was invited to Valve headquarters to see the device, and reported that its chassis is just a little bigger than an Xbox 360, but smaller than any gaming PC.

Inside is a giant Nvidia GeForce GTX Titan graphics card and a full desktop CPU, and the system is cooled via vents on the top for the CPU, the side for the power supply, and the back for the graphics card.

During the visit, Valve also discussed the dozen or so prototypes of its Steam Controller, which included a magnetic break apart Xbox 360-style controller, a Wiimote-like peripheral for each hand, an early design with a touch screen, and several versions containing a trackball.

Biometric sensors were discussed but never made it in because Valve found moving hands weren't a good source of biofeedback, however the company hinted that an unannounced VR headset it is working on could measure your reactions at a player’s earlobe.

One thing that did make it into the Steam Controller is a gyroscope, which Valve said will likely be activated via a patch following the controller's release.

Valve is only building the prototype Steam Machine as a reference design. Consumer Steam Machines manufactured by a range of hardware partners will be unveiled in January at the Consumer Electronics Show, along with the games that will come to the Linux platform.

Steam Machines a quarter of the size of the current prototype are expected mid-2014, and will house integrated graphics rather than a separate graphics card.