Obviously, a desk-side tower with attached display and peripherals is a PC. All-in-one machines running Windows certainly qualify, as do most laptops. But what if the device is a tablet running Windows RT, Microsoft’s upcoming OS for ARM-based systems? No one would call the iPad a PC, yet the Microsoft Surface RT and similar Windows RT tablets will include some flavor of Microsoft Office--an application that’s strongly associated with PCs.

An Ultrabook running Windows is certainly a PC. But what about a Chromebook running Chrome OS? It’s almost always connected to the cloud, and doesn’t run Windows--but it’s certainly capable of running applications that most business PC users would recognize. And the new Surface Pro may be extremely thin and light, but it’s a PC all the way down to its x86 CPU and its ability to run most Windows applications.

As the PC evolves, we'll see the emergence of new products that push the definition of the personal computer. In some cases, hardware that most of us wouldn’t call a PC will run applications traditionally associated with personal computers, just like those Windows RT tablets that run Office.

If the new PC generation simply consisted of experiments like Lenovo’s IdeaCentre A720 and marketing initiatives like the Ultrabook, we’d see the PC as merely evolving with the times. Windows 8 and Microsoft’s Surface tablets, however, lay out a different vision of the PC’s destiny. Apple may have defined what the tablet could be with the iPad, but Microsoft is defining the future soul of the PC.