Facebook today formally announced a long-rumored deal to acquire Microsoft's Atlas Solutions division today and that its interest in the technology stack boils down to measurement.

Ad Age previously reported that Facebook had agreed to buy the ad-serving business, which Microsoft had busily been seeking a buyer for over the past six months. Microsoft has acknowledged that it's looking to focus on developing the ad business for its owned and operated products like xBox and Windows 8, not on its ad tech.

The deal price was not disclosed, and the parties would only say that a "commercial agreement" will be put in place whereby Microsoft will continue to buy its own ads through Atlas. The price had been expected to be less than $100 million, based on prior bids for Atlas, which were in the $30 to $50 million range.

Atlas had looked like a potential building block for Facebook to start building an external ad network powered by its social data, but the social network's director of product marketing Brian Boland said that's not the plan. He said that Facebook's advertisers have been clamoring for more tools to let them see how effective their spend is across online channels, and that's where Atlas comes in.

Facebook has been steadfast that the effectiveness of its ads shouldn't be gauged by clicks alone. Owning an ad server will allow the social network to track actions after a user is exposed to an add, so-called "attribution." Atlas can help Facebook prove that exposing users to its ads does spur them to take an action – whether it's providing their email address or making a purchase – even if they've never clicked on a Facebook ad. Atlas released a tool last year to help advertisers measure their Facebook ads and get into deeper insight into how they drove conversions.

"This acquisition is about measurement, it is not about building an ad network," Mr. Boland said, adding that Facebook intends to invest in Atlas's core technology, as well as new areas like mobile ROI. He acknowledged Atlas's reputation in the marketplace for having antiquated technology due to years of neglect.

"We're excited to apply the same level of focus and investment in Atlas that we've applied to mobile over the last year, and really accelerate the development of its core features," he said.

Mr. Boland declined to say whether all Facebook advertisers would eventually be given access to Atlas's measurement tools. He noted that Facebook will continue to support existing Atlas customers -- comprised of agencies, major marketers, and publishers like Microsoft -- in their contracts.

Atlas's team will continue to be based out of Seattle, which is also where most of Facebook's engineers who develop ad products are based. "Most if not all of Atlas's employees" will join Facebook in the deal, Mr. Boland said.