Top Windows chief Steven Sinofsky took to a company blog to announce the availability of Release Preview, and along the way cited all kinds of impressive numbers, ranging from "hundreds of millions of hours of testing" to an accounting of the often-verbose blog.

But the Release Preview isn't the final code, Sinofsky warned.

"We will still be changing Windows 8," he said, referring to the time between now and RTM, or "release to manufacturing," the stage where code is handed over to computer makers to begin installing on new systems.

No kidding.

While Release Preview is a step up from February's Consumer Preview, it shows rough spots and has some important unfinished business, among the latter a more complete reworking of the user interface (UI) to ditch Vista's and Windows 7's "Aero" look-and-feel.