To execute a mobile ad buy, you have to choose between various networks and exchanges and real-time bidding platforms. The ads themselves are also different since they're often designed to prompt users to take action relatively quickly, which mean fewer branding ads and more direct-response executions. To ensure that the ads are effective, it helps to tailor to them to individual users' demographics and geographic location. To make things even more complicated, while on desktop, there are basically two operating systems, in mobile there are at least 10, Becker says and "hundreds of browsers and screen sizes."