Facebook uses a variety of server types across different parts of its data centers, but the company's aversion to virtualization extends throughout its infrastructure, Coglitore said.

"We find in our testing that a realized environment brings efficiencies and brings the ability to scale more effectively," Coglitore said. "If virtualization was the right approach, we would be a virtualized environment."

Facebook wants to be able to balance its computing load across many systems and potentially lose a server without degrading the user experience. "As you start to virtualize, the importance of that individual server is greatly enhanced, and when you have that at scale, it becomes very difficult," Coglitore said. He prefers to think of computing units as faceless, interchangeable "foot soldiers." Virtualization makes it harder to treat hardware resources that way, Coglitore said. Using a virtualization software layer also tends to create lock-in, he said.

In addition, though Facebook could take advantage of more powerful server platforms for some functions, it sometimes turns to lower end systems for budgetary reasons. Facebook prefers to change servers every two to three years, following the chip refresh cycles of Intel and other processor makers, Coglitore said.

Intel currently ships a 45-watt Xeon and a 30-watt Xeon processor for microservers. Upcoming microserver chips include the 45-watt E3-1260L and 20-watt E3-1220L, which are already shipping to server makers, and a unnamed 15-watt part based on the new Sandy Bridge architecture. The Atom-based, sub-10-watt microserver processor coming next year also does not yet have a name, Intel's Davis said.