AOL has agreed to acquire Gravity, a software startup that tracks users to show them ads and content more relevant to them. The acquisition, for at least $83 million, includes Gravity’s personalization technology and more than 40 employees, AOL Chief Executive Tim Armstrong said in an interview. AOL will pay an additional $7.7 million two years after the deal closes, and will assume about $12 million of operating loss though it would result in a future tax benefit of $5 million, the company said in a press release. The move marks Armstrong’s fourth-largest deal since taking the reins of the troubled Internet portal in 2009, a period in which he has led a shift towards ad-supported content. By plugging Gravity’s technology into AOL’s hundreds of news sites, blogs, videos and mobile apps, the company hopes to keep users around for longer periods of time and viewing ads tailored to them.