PRINEVILLE — A 147,000- square-foot data center has taken form during the last sixth months, replacing about three acres of juniper trees in Prineville with tons of steel and concrete, not to mention hundreds of construction workers.

PRINEVILLE — A 147,000- square-foot data center has taken form during the last sixth months, replacing about three acres of juniper trees in Prineville with tons of steel and concrete, not to mention hundreds of construction workers.

Within the next six months, Facebook plans to complete the initial phases of its first company-owned data center, filling out the skeleton that's now standing on 124 acres of rural land the company owns off Tom McCall Road.

Though the 125 to 175 construction workers who are on site daily may be gone at the beginning of 2011, when the first two phases are finished, more work could come if membership keeps growing at www.facebook.com, thus requiring the social-networking company to expand the data center, as much as doubling it in size.

"We've got to be right in front of our users' demand," said Ken Patchett, Facebook's recently hired director for the Prineville data center. An extension of the main building "has always been in our wheelhouse."

Data centers are the heart of online computing, pumping tremendous amounts of information every second through and storing it in the computer servers that allow websites to run smoothly. Facebook's servers host its users' thousands of pictures, comments and increasing numbers of applications and games, among other information.

Facebook currently rents out space in data centers in California and Virginia, and the Prineville building will be the first company-owned facility for hosting its computer servers. It's being built in response to its already growing user base.

When Facebook announced the project in January, officials said it had 350 million users. At the end of May, Time magazine wrote that Facebook would soon have 500 million.

As it stands today, the center is a two-story cement building that can be seen poking above the horizon and smaller structures off state Highway 126. It's a dusty construction site with enormous piles of dirt, rock and gravel salvaged from laying the building's foundation.

Though the data center is still a shell, it's nearing completion at a seemingly exponential rate. Cement walls stand today and roofers are on site, while only steel structural beams were erected two months ago.

Workers this week are installing gateways from the second story of the building that will carry outside air into the center's core, used to cool Facebook's rows of servers. Use of outdoor air is a primary reason Facebook chose Prineville. Even during higher summer temperatures, the servers can still be cooled by the air.

The air-cooling system also is a reason the building will qualify for Leadership in Energy and Environmental Design, allowing the company to save money on air conditioning costs. The rows of computer servers can easily overheat and must be cooled to continuously operate.

While the top floor of the data center will only be used for its cooling system, the bottom floor will hold a lobby, office space for its staff and, initially, two nearly identical rooms for the computer servers.

Those rooms, known as phases 1-A and 1-B of the data center, take up the majority of the 147,000 square feet of the building. Though they're empty now, save construction equipment, Patchett said he may be able to start installing servers into 1-A by the end of 2010, after construction crews finish it and focus on quickly completing 1-B. That means millions of Facebook users' communications could begin flowing through Central Oregon after the new year.

The possibility of building two more sections in future years, 1-C and 1-D, is the reason Facebook purchased so much land. Through Vitesse LLC, the entity Facebook used to do its footwork locally, Facebook paid $3.2 million in January for the 124 acres.