Google and Microsoft are now officially fighting over you. They are vying not merely for your momentary attention—that rare instant when your precious eyeballs stray to an ad, motivating you to click on it and cause a penny or a nickel to fall into their jars. They want a long-term relationship with you, and each thinks its future depends on it.

Google made its boldest bid in this direction this week with the announcement of its new operating system, Chrome. Soon you will be able to buy a PC or other device loaded with Chrome instead of Windows. By Google's account, Chrome will serve a single essential purpose: to get your computer up and running with a Web browser —confusingly also called Chrome—seconds after you've turned it on. Now you'll be greeted each day by Google instead of Microsoft. Just as all those years ago Microsoft Windows pointed you toward Microsoft's other products, Google's browser will likely naturally angle you toward Google's ever-expanding family of Web products.

If the plan succeeds and lots of people snap up Chrome instead of Windows, it will cement the idea that software is now meant to run out there "in the cloud," far away from the PC or PDA in front of you. You'll need an Internet connection to do most things—and to be sure, that's much easier to find in 2009 than it was in 1995. The question is, in the era of the cloud, how do we avoid sacrificing our essential computing freedoms?

The issue arises because Google aspires to be not only the index of your information, but also the repository. As Google Mail seamlessly interacts with Google Docs and Spreadsheets (the whole service is called Google Apps), you might find yourself spending most of your time not simply on the Web, but at Google.com or its partners. Google could be as dominating a presence in the cloud era as Microsoft has been in the PC era.

Google's announcement is a milestone within a long transition from the PC to the Web. For about two decades, an overwhelming majority of computer users were greeted by Microsoft's Windows startup screen and chime. Microsoft collected fees for the basic software that ran your PC, and then again by selling application software such as word processors and spreadsheets. Software developers would write new software for Windows since that's where the users were, and users would keep buying Windows since that's where the software was. As the Web took off in the late 1990s, the browser began to disturb this arrangement. Netscape got the idea of bundling software called Java with its browser, which made it powerful enough to take on word processing, spreadsheets, and many other things.

Google is now on the verge of finishing what Netscape started. So far, Google hasn't fully figured out its business model. Instead of charging you the way Microsoft did for Windows and Office, perhaps Google will stick with ads, hoping you'll occasionally click on something. Or perhaps, serving as the hub of your online identity, Google can help you spend your money on other sites, taking a cut the way your credit-card company does from a merchant when you make a purchase. Or perhaps Google will charge developers for the privilege of running their software on the Google Apps platform, or even to run it elsewhere but drawing upon Google resources—the way that a restaurant's Web site might help you find the place by embedding an interactive Google map on one of its pages.

Although no one can predict Chrome's future, the Web relentlessly pulls us, and our data in. Unless we come up with ways of protecting ourselves now, our data could be shaped and used in ways we haven't imagined and that are beyond our control. We could find it hard to switch from one service provider to another after piling up so much information, and so many relationships, in one place. We ought to be able to move our data, with just a click, from one gated community to another—from, say, Microsoft's Office Live, its suite of Web-based software, to Google Apps. We ought to be able to bridge our identities from one place to another, instead of having to choose just one. Why shouldn't our Google Docs be permanently accessible through Office Live and vice versa, and on to some upstart site that no one's heard of? Market forces may naturally take care of this—but they are not magic, and a little bit of well-crafted regulation (or the threat of it) can help maintain a competitive marketplace.

Freedom for you is one half of the puzzle. The other half is freedom for those who write software. Even in a world mostly of Windows, there are thousands of different pieces of software that can be found, and Bill Gates has had nothing to say about whether they would be allowed to run on his platform. We ought to preserve similar freedoms in a new world where Web platforms can and do shut down outside software all the time, whether on the Facebook platform or Google Apps. This might come about through software authors uniting to temper some of the practices that give Web-platform makers much more control over outside software than Microsoft ever had for its desktops, or again, through narrow regulation to ensure nondiscriminatory accessibility to these platforms—especially if one platform outgrows the rest.

Long-term relationships can be extremely valuable and healthy; it makes sense to get new and promising ones off on the right foot.

Jonathan Zittrain is a professor of law at Harvard Law School and faculty co-director of Harvard's Berkman Center for Internet and Society. He is author of The Future of the Internet—and How to Stop It.

© 2009