The 300 Steam Machine prototypes that Valve will be sending to Steam users later this year will be high-end computers built from off-the-shelf PC parts, the company announced today.

Here's the list of hardware specifications for the prototype, which will run Valve's Linux-based SteamOS:

GPU: some units with Nvidia Titan, some GTX780, some GTX760 and some GTX660

CPU: some boxes with Intel Core i7-4770, some Core i5-4570 and some Core i3

RAM: 16 GB DDR3-1600 (CPU), 3 GB DDR5 (GPU)

Storage: 1 TB / 8 GB hybrid SSHD

Power supply: internal 450 W 80 Plus Gold

Dimensions: approx. 12 inches x 12.4 inches x 2.9 inches high

For comparison purposes, the older PlayStation 3 Slim (not the current "super slim" model) measures 11.4 inches by 11.4 inches by 2.6 inches. The unit comes in a custom enclosure, and Valve will release the CAD source files for the design in case users want to replicate it.

"We wanted to accomplish some specific design goals that in the past others weren't yet tackling. One of them was to combine high-end power with a living-room-friendly form factor. Another was to help us test living-room scenarios on a box that's as open as possible," said Valve's Greg Coomer in a post on the Steam forums.

Coomer also pointed out that the various Steam Machines that third-party manufacturers will release in 2014 may differ, "in many cases substantially," from the components and form factor of the prototype.

the prototype may be "the kind of machine that a significant percentage of Steam users would actually want to purchase"

"To be clear, this design is not meant to serve the needs of all of the tens of millions of Steam users," Coomer continued. "It may, however, be the kind of machine that a significant percentage of Steam users would actually want to purchase — those who want plenty of performance in a high-end living room package."

In addition, said Coomer, the prototype isn't designed as a replacement for an existing gaming rig.

"Many of those users would like to have a way to bridge the gap into the living room without giving up their existing hardware and without spending lots of money," said Coomer, adding that the in-home streaming supported by SteamOS will facilitate that.

Valve isn't ready to share images of the prototype's case, since the design hasn't been completed yet. But according to Coomer, the company will soon provide some "closer looks" at the Steam Controller.