(CNN) -- Microsoft is taking its last big step before releasing what promises to be a massive overhaul of its Windows operating system -- and, by extension, how almost all devices running it work.
Nearing the end of a long process of tinkering under the hood, the computing giant on Friday rolled out its final preview of Windows 8, which is expected to go on sale this fall.
"Since our first preview release last September, millions of people now use the pre-release product on a daily basis and millions more have been taking it through its paces, totaling hundreds of millions of hours of testing," Microsoft's Steven Sinofsky wrote Friday on the Windows 8 blog.
"We genuinely appreciate the effort that so many have put into pre-release testing, and of course, we appreciate the feedback too. Direct feedback and feedback through usage contributed to hundreds of visible changes in the product and tens of thousands of under-the-hood changes."
The post said Microsoft has received about 18,000 comments from 7,000 early testers of Windows 8, which have contributed to "hundreds of visible changes in the product and tens of thousands of under-the-hood changes."
The release will mark the first major update of Microsoft's operating system since Windows 7 was released three years ago. Unlike previous releases that have, essentially, revamped (or, in at least one case, mercifully killed) existing features, Microsoft is touting Windows 8 as a radical reimagining of its core product.
Perhaps its most visible difference from previous versions of Windows will be its compatibility with touchscreen technology. That, combined with the system's ability to connect devices (say, a PC, a tablet and a Xbox gaming console) is what Microsoft hopes will renew the enduring Mac vs. PC war on a new front.
"In our hands-on of Microsoft's Consumer Preview, we declared that your familiar Windows desktop is all but dead," Alexandra Chang wrote Friday for Wired.
"In the changes we've seen in the Release Preview, this still holds true," she added. "Microsoft is focused on improving and deepening the Metro [the system's design language] experience, where the desktop is only a portion -- or even an afterthought, for some users -- of a larger, app-based system."
The company has made something of a ripple with its smartphone system, at least among critics. The recently released Nokia Lumia 900 has been heralded as the best Windows phone ever, although, as of March, only about 4% of U.S. smartphones ran the company's operating system. (For what it's worth, that's a month before the Lumia was released.)
But Microsoft has barely moved the needle in the tablet space, where Apple still rules the roost, and only a simpler and less expensive device like Amazon's Kindle Fire has been able to put up much resistance.
Even as the final Windows 8 trial was being announced, reports were surfacing that Asus, Toshiba and Acer all plan to unveil Windows tablets next week at the Computex trade show in Taipei.
Meanwhile, many in the tech world are watching and waiting. With its prowess in the computing world, it's impossible to count Microsoft out. But with Apple and Google's Android system grabbing the attention and market share in the mobile world, Microsoft appears to have an uphill battle.
"There's a long, narrow road ahead for Windows 8," reviewer Seth Rosenblatt wrote for CNET. "It could be the next big thing, but there's not much room for missteps."