It feels like a long time since we've had a great big knock-down, drag-out operating system battle. Windows vs. Mac shook out in the ’90s. iOS vs. Android is mostly settled. But another one is starting this summer if you know where to look. It's not in classic PCs, where the relative qualities between Mac and Windows have remained stable for some time now. It's not in phones, where the iPhone is dominant at the high end and Android owns massive marketshare.