Google has announced that it intends to sell Motorola to Lenovo for $2.91 billion. Google CEO Larry Page said that Google will hold onto the vast majority of Motorola's mobile-related patents, and will continue to use them to defend Android's position in the smartphone ecosystem. Lenovo plans to keep the Motorola brand alive, just as it did with the ThinkPad brand it acquired from IBM in 2005. According to Page, Google believes Motorola needs a hardware company to truly succeed. "Lenovo has the expertise and track record to scale Motorola into a major player within the Android ecosystem. They have a lot of experience in hardware, and they have global reach," said Page in a blog post. "This move will enable Google to devote our energy to driving innovation across the Android ecosystem, for the benefit of smartphone users everywhere." The deal will need to be approved by regulators in China and the U.S., and will take some time. Page did not say when he expects the deal to close.

Motorola was purchased by Google at the end of 2011 (with the deal closing in the Spring of 2012) for a pretty hefty $12.5 billion. That's a large delta from the $2.91 billion that eventually changed hands between Google and Lenovo today, but those two numbers don't quite tell the entire story. Considering Motorola's handset portfolio and sales leading up to the point when it was sold to Google, the assumption was that a big chunk of that $12.5 billion was for the company's patent portfolio. Indeed, Google valued Motorola's vast array of patents at a sizeable $5.5 billion shortly thereafter. It makes sense then that Google chose to hold onto these patents when it eventually sold every other part of Motorola to Lenovo.

So $2.91 billion from Lenovo, plus $5.5 billion worth (to Google) of patents. That's $8.41 billion of value, which comes up short of the $12.5 billion it paid initially. But in the end, Google didn't finish the deal $4.09 billion in the hole — there's far more to this balance sheet.