The “post-PC” world that Steve Jobs imagined is closer than many expect. All it needs is for the major mobile platform makers to subtly shift their offerings to meet the needs to more sophisticated productivity scenarios. If they do, the PC market will contract even further.

Today, this market is dominated by traditional Windows PCs, of course. And yes, Google’s Chrome OS and Apple’s macOS vie with Windows, though neither has been able to loosen Microsoft’s death-grip on the market: Macs still account for well under 10 percent of all traditional PCs worldwide. And Chromebook? It’s part of the “other” category, with about 0 percent market share, though I’ve been told by PC makers that the system is very popular in U.S. education.

What both Google and Apple have, however, are secret weapons that Microsoft lacks: Incredibly popular mobile platforms. And as these platforms mature, they are becoming increasingly viable PC replacements. And it won’t take much to put them over the top.

Microsoft, of course, has tried, but failed, to match the mobile efforts of its competitors. But with Windows RT and Windows phone utterly failing in their respective markets, Microsoft has an exposed flank. And while it’s fair to say that Windows 10 has done a credible job of reestablishing Microsoft’s presence in the PC market, it hasn’t (yet) helped with mobile.

The issue, of course, is apps. And where Microsoft’s Windows 10 and Windows phone are still precarious from a mobile app perspective, Apple iOS and Google Android have steadily improved on the productivity app side. Ironically, they’ve done so with Microsoft’s help: The Microsoft Office apps, in particular, not to mention its ever-growing collection of other apps for Android and iOS, are both excellent and full-featured. What Android and iOS are missing, however, are platform features that make those systems more suitable for the traditional productivity tasks that we now perform on PCs.

Surely—surely–those shortcomings will soon be addressed. And it’s not coincidental, I think, that both Google and Apple have shipped in the past six months devices—the Pixel C and the iPad Pro, respectively—that can replace traditional Windows laptops. All that’s missing, of course, is a bit of sophistication in the underlying software.

And sitting here on the cusp of that revolution, we can finally see how Microsoft’s Windows phone and Windows RT failures have deeper ramifications than just the smart phone and tablet markets: It is much easier to improve mobile platforms enough to replace PCs than it is to try and simplify PCs and make them more suitable for mobile usage scenarios. Especially when you have Microsoft helping you on the app side of the equation. Imagine how much of a blocker it would be for enterprises if Microsoft Office wasn’t already available on Android and iOS.

Microsoft can of course promote the fact that Office is even more full-featured on traditional PCs. And that’s true enough. The problem is that it doesn’t matter, because most people don’t need the vast majority of esoteric features that pad out those desktop Office applications. The audience that needs these features is likely comparable to that for engineering, CAD/CAM, graphic arts, music creation, and software development solutions. Which is to say, small. Lucrative, maybe, to smaller software companies. But small.

(This, by the way, is why the Office Mobile apps require an Office 365 subscription on larger-screen devices. You still need to pay to use Office if you’re going to use these apps for real productivity work.)

So what’s needed? Not much, really. Better multitasking user experiences, where apps can be arranged not just side-by-side on screen, but also in floating windows. And some kind of a cursor and pointing hardware instead of just touch and pen. Put simply, content creators need more sophisticated ways to interact with the system than we see today in Android or iOS.

But that’s changing. And today, Android appears to be closer to this future than iOS, as we already know that Android N will support a windowing mode for apps that goes far beyond the restrictions of side-by-side full-screen apps. But both Google and Apple will soon hold their annual developer events—Google I/O in late May and WWDC in mid-June—so it is possible, if not likely, that we’ll find out more about their plans to kill the PC once and for all at these shows.

Folks, this is a potential extinction moment, with Android and iOS playing the role of the asteroid that is hurtling to earth to kill off the Windows dinosaurs. And if you think PCs are a small part of personal computing today, it’s only going to get worse a few years down the road as an entire generation of Google-services-using, Apple-hardware-wielding youngsters streams into the workforce expecting to use the tools they’re familiar with. Our children are not growing up on Microsoft technologies. To them, Microsoft is as relevant as Sears, AOL or IBM.

This is, of course, why Microsoft pushes Windows 10 adoption so aggressively, and is willing to aggravate users to achieve its goal of a billion-plus users. It’s why Microsoft is pushing Windows 10 beyond the PC, and isn’t giving up on mobile even though it’s already lost. And it is why Microsoft’s cloud push is so important to the future of the company: As its consumer- and client-side offerings become less important, Microsoft can find great success as a maker of back-end systems that are used, silently, everywhere. Like electricity. That’s powerful, but not of particular interest to us hardware enthusiasts.

Look, I love Windows 10. I prefer PCs to Macs and Chromebooks. And I very much prefer Windows 10 to Chrome OS and macOS, and to Android and iOS for that matter. But the future of personal computing, as we know it, is no longer being determined by Microsoft, I think. And it’s only a matter of time before Google and Apple step up to the plate with more mature mobile offerings that will spell real trouble for Microsoft’s desktop platform.