How do you reinvent the PC for the tablet era? Asks Time.com. Microsoft [1], not surprisingly, has been spending a lot of time mulling over that question in recent years. Its touch-centric new operating system, Windows 8 [2], is largely devoted to answering it. And for the first time ever, the company decided to show us exactly what it thinks a modern PC/tablet hybrid should be by designing and selling its own Windows computer, Surface. Except it didn’t come up with one Surface — it built two of them. The first version, Surface Windows RT [3], shipped in October, simultaneously with Windows 8. Technically speaking, however, it isn’t a Windows 8 machine: It uses a power-efficient ARM processor and a special version of Windows called Windows RT which only runs new programs designed for the touch-friendly “modern” interface, not all the apps written for conventional PCs. Starting at $499, it’s the closest thing Microsoft has to a direct iPad [4] competitor…