An efficient platform
With the graphics and CPU choices made, let's turn to the platform: motherboard, memory, case, and power supply. The motherboard must support the LGA 1155 Core i7 3770s CPU, and will dictate the physical size of the case. The system needs an adequate amount of memory, and anything to help power efficiency is a bonus. The case should be small enough to sit on my A/V rack, but large enough to ensure adequate airflow. Finally, the power supply must be efficient and quiet.
Motherboard - Asus P8Z77-I: This Steam box runs on an Asus P8Z77-I Mini-ITX mainboard. The P8Z77-I sports two DDR3 memory sockets, on-board Wi-Fi with Intel WiDi (Wireless Display) capability, Bluetooth, and a bunch of USB ports. One cool design decision by Asus was to put the VRMs (voltage regulator modules) on a separate riser board on one side. The riser board is attached with screws that also serve as mounting screws when you attach the entire affair to the bottom of the case. The rear of the board includes graphics ports (in case you're using integrated graphics), USB ports, and antenna connections for Wi-Fi.
That's a nice feature set, but the strongest reason to pick the P8Z77-I is its compact size: We can build this Mini-ITX board into a really small chassis. The board also has one PCI Express X16 slot for a high-performance graphics card, so it can accommodate the GTX 660 Ti just fine.
Memory - HyperX LoVo DDR3 RAM: I've used Kingston HyperX LoVo low-voltage DDR3 in past projects, and it has consistently delivered good performance. At 1.35 volts, it demands less power than the typical 1.5 volts required by standard DDR3 and much less than the 1.65 volts that some high performance modules need. Yet the price premium over standard DDR3 is fairly modest. An 8GB kit consisting of two 4GB modules costs less than $60, which is competitive with the prices of other high-quality DDR3 modules.
Case - Coolermaster Elite 120 Advanced: The numerous Mini-ITX motherboards available have spawned a large number of compact cases. In an ideal world, I would have found a suitable low-profile case, but in the world we've got I would have had to sacrifice too much graphics performance to get the dimensions I preferred. In the end, I narrowed my options down to three cases: the Silverstone SG06, the Fractal Designs Node 304, and the Coolermaster Elite 120 Advanced. The SG06 was the smallest of these, but I had concerns about the 300W power supply, and the 10-inch Asus graphics card looked problematic, too. The Node 304 is pretty massive for a Mini-ITX case, yet it lacked an optical drive slot (it would have been a great choice if I had been building a small server). The Coolermaster Elite 120 Advanced is almost as large as the Fractal Design case, but it's the one I chose in the end.
The Elite 120 can handle a 10.5-inch graphics card; and since the Asus GTX 660 Ti is a nonreference card that's a bit longer than most, having the extra space proved useful. The Coolermaster also accepts a full-size ATX power supply and full-size optical drive. Tool-free installation of storage hardware is an added bonus.
Power supply - Seasonic SS520-FL: High efficiency and low noise are key requirements for a power supply destined for service in in a living-room PC. Seasonic's SS520-FL is a passively cooled, fanless power supply with an 80-Plus Platinum efficiency rating--meaning that the SS520-FL is 90 percent efficient through most of its range, dipping below 90 percent (to 89 percent) efficiency only under 100 percent load. My little Steam box will never demand 100 percent from a 520-watt PSU, so it should perform at peak efficiency.
The Seasonic PSU offers the added benefit of having modular connectors, so I could install only the power connections I needed. As it turns out, I ended up needing most of them, but I was able to leave one aside. And any reduction in power-supply cabling means less clutter and better airflow through the already crowded case.
For the CPU cooler, I needed something compact and quiet, and yet able to get the job done. Silverstone makes a low-profile LGA 1155 cooler, the NT07-1156, that can handle CPUs rated at up to 95 watts. It also has a small switch on the side to run the fan a little more slowly, for lower noise. That's what I used for the 65W Core i7-3770s CPU.
Primary hard drive - Crucial M4 512GB SSD: Given that my Steam box will be running games, the system must offer enough storage to hold a number of games--and modern PC titles can consume a lot of space. At the same time, low power and low noise are essential. I went with the Crucial M4 512GB solid-state drive. I've used this SSD in other systems, and it's been admirably reliable. It's not the best-performing SSD you can buy, but it's relatively inexpensive, at under $400, and it's plenty fast for my needs, especially when compared to the standard disk-based hard drives found in most PCs and gaming consoles.
Optical drive - Asus BW-12B1ST Blu-ray: If I were running nothing but Steam games, the system wouldn't need an optical drive. But I occasionally buy games on optical media, and not all great games are sold on Steam (yet). By dropping in a Blu-ray drive, I can also use the system to play Blu-ray movies on the 60-inch LG plasma HDTV hooked up to this PC. I chose the $80 Asus BW-12B1ST Blu-ray writer because it packs a lot of capability into a Blu-ray drive, including 8-12X Blu-ray write speed and 16X DVD-R write speed.