The Windows ship is leaking in a dozen places, pierced beneath the waterline by very pointy iPads. Where the Mac never really made a dent in Microsoft's PC hegemony, the iPad is doing so: it's being handed to children as a first computer, appearing in schools, and running point-of-sale systems for small businesses. If you consider the iPad a PC, then Apple's the No. 1 PC maker , according to research firm Canalys. That makes the iPad public enemy number one for Microsoft if it intends to maintain its PC leadership, and the new Surface tablet is Microsoft's primary weapon. Surface comes in two versions. The Windows RT version matches the iPad on price, but has relatively few apps; all the same, this will be the model at which most consumers look. The more-expensive Windows 8 "Surface Pro" version will run existing business software. I hate calling things a "such-and-such killer," but Microsoft needs to at least slow the iPad...