The Windows operating system that Microsoft (NASDAQ:MSFT) should've rolled out a year ago is finally here.

Windows 8.1 became available for download today. It will show up at retail stores tomorrow. The reviews are generally favorable. The Start button -- the feature that threw most early adopters for a learning curve loop -- is sort of back as an option. The same Live Tiles that have made Windows 8 seem like a blown-up version of Windows Phone are still there, but the new interface is easier to customize. It no longer feels as awkward if you don't happen to have a touchscreen. 

Investors shouldn't expect a deluge of new PC buyers to emerge for this rollout. Global PC shipments have fallen sharply every quarter through each of Windows 8's first 12 months on the market, but it's not necessarily Microsoft's fault. In fact, Apple's actually been doing even worse. Shipments of Macs and MacBooks have fallen harder than Windows-fueled PCs. Take out Apple and domestic shipments actually improved during the quarter!

With momentum building closer to home this could be the push that Microsoft was hoping would happen last year. However, Windows 8.1 still doesn't solve the problem that the tablet and smartphone markets are growing fast at the expense of desktops and laptops. In terms of computing -- mobile or PC -- Microsoft's Windows is losing market share to Android and Apple's iOS. A well-regarded and necessary update isn't going to change that. Too many former PC buyers have come to realize that they never needed the sheer processing power of a traditional computer. Outside of the corporate world and the ranks of designers and die-hard gamers, tablets and smartphones will do just fine in scratching the itch of email checks, casual games, and surfing the Web. 

Why do you think Steve Ballmer is stepping down as CEO? Why do you think Microsoft is shifting its emphasis to become a devices and services company? Apple, Microsoft, and nearly every box maker has moved to adapt to the mobile computing future and what it means for their core businesses. In Microsoft's case, we're talking about a world that's moving away from its proprietary operating system to the more cost-effective open source Android. 

So, yes, Windows 8.1 is here. It's a year too late, but Microsoft itself may be several years too late at this point.

Longtime Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool recommends Apple. The Motley Fool owns shares of Apple and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.