This year, Microsoft and Apple are both introducing new versions of their operating systems with important changes to their user interfaces, and with a flurry of publicity. A third major company is also overhauling its PC operating system, but you probably won't hear much about it.

Google redesigned its PC operating system, Chrome OS. While Google is a major rival to Apple and Microsoft in things like search, smartphones and browsers, Chrome OS hasn't dented the competition in the year since it emerged. It was meant to be radically different than Windows and the Macintosh operating system, a refreshing change for a new era. But it had serious limitations, principally that it ran only apps inside a browser on a handful of special, low-powered laptops called Chromebooks and could do almost nothing when it wasn't online.

The new version, which I've been testing, aims to address some of those issues and it makes some progress. But I still can't recommend it over a PC or Mac for average consumers who are looking for the greatest versatility in a laptop. I still find it more of an evolving project than a finished product.

Its fundamental limitations remain. Most importantly, you still can't install your favorite programs, be they Microsoft Office or iTunes or Firefox—only a few thousand "Web apps" that run inside the Chrome browser. And it still only works on specific hardware: that laptop called the Chromebook or—new this year—a small desktop called a Chromebox. The only hardware maker producing the 2012 versions of these machines so far is Samsung, though Google says more are coming.

Chrome OS does have some admirable qualities—especially its philosophy of simplicity and of being wedded to the cloud. For instance, because it's designed to fetch your apps and documents from the Internet, you can replicate your entire computer by just logging in on any other Chrome OS PC. And, if you mainly use the Web and live in the cloud, it may be the ticket for you, especially as a second machine.