Close your eyes and imagine it’s five years from now. Now, check your pockets and your desk. Which devices are you using?

It’s very likely you have a smartphone. But is your second device an iPad-like tablet or a more traditional PC? Or perhaps you have a laptop-tablet hybrid, like Microsoft’s Surface? Or maybe you don’t own a second device, because your phone is powerful enough. Or you might have everything, because that’s how you roll in our hypothetical future.

O.K., open your eyes and get back to the present. If you had any trouble choosing, you have a taste of the dilemmas facing Apple, Google and Microsoft, the three players waging an epic battle for the future of computing.

Technology now allows for lots of powerful, compelling computing devices in a wide range of sizes and shapes. Just about everyone in the industry believes the smartphone will remain the dominant computing device for the foreseeable future. But second place looks entirely up for grabs, and the giants are jockeying to make that one other device that we’ll all use along with our phones.