Analysts from Gartner and IDC say that PC sales dropped about 8.45 percent in the third quarter of 2012, the most precipitous drop in PC sales since 2001. And both firms agree on the cause, too: The market is preparing for the launch of Microsoft’s ambitious new Windows 8, which will dramatically and permanently move the PC market closer to that of mobile devices.

“The third quarter was a transitional quarter before Microsoft's Windows 8 operating system release, so shipments were less vigorous as vendors and their channel partners liquidated inventory,” Mikako Kitagawa explained in Gartner’s report about third-quarter PC sales.

"We expected a weak PC market in the lead up to Windows 8 release in the fourth quarter,” David Daoud noted in IDC’s report about third-quarter PC sales. “While the industry has been focused on shaving excess inventory and preparing to launch a new generation of products, consumers have been looking at alternative devices like tablets. Nevertheless, as vendors line up innovative new products and designs, consumers are likely to respond positively during the tail end of 4Q12, and that means a potential return to positive growth at the end of this year.”

Aside from the nosedive in overall PC sales, this quarter was significant because it marks the first time ThinkPad-maker Lenovo edged out struggling HP for the top spot. By all accounts, it won’t be the last: HP CEO Meg Whitman revealed recently that she expects her company to reel for a few more years before order is restored. And Lenovo, unlike HP, is embracing the PC-plus world of the future by announcing a full lineup of tablets and hybrid devices based on Windows 8 and Windows RT. HP had been the number-one PC maker in the world since 2006.

Averaging the two firms’ numbers, as is my custom, we see that PC makers overall sold 87.6 million PCs in the quarter. The top five PC makers worldwide are Lenovo (13.8 million units), HP (13.75 million), Dell (9.3 million), Acer (8.5 million), and ASUS (6.4 million).

In the United States, as always, the picture is dramatically different, with Apple making an appearance in the top five. Again averaging the firms’ numbers, we see that an estimated 15.8 million PCs were sold in the United States during the third quarter of 2012. The top five PC makers in the United States are HP (4.2 million units), Dell (3.3 million), Apple (2 million), Lenovo (1.4 million), and Acer (1 million).

Looking ahead, there are of course questions, and they begin with Windows 8, a confusing new platform from Microsoft that—despite its name—actually bridges the mobile computing world with the traditional PC market. But Gartner claims that although tech-savvy Americans are debating tablet purchases and a coming generation of hybrid devices, the real growth in the PC arena of the near future will be due to emerging markets. Almost 70 percent of PC sales are expected to come from emerging markets in 2016, up from about 50 percent in 2011.

Microsoft, somewhat infamously, is bullish about the future and about Windows 8 specifically. Microsoft Vice President Keith Lorizio said earlier this week that his company expects to sell more than 400 million units by July 1. A Microsoft spokesperson later reached out to me to clarify that statement, noting that the 400 million figure was from a previous IDC prediction of PC sales through July 1 (for a full year, from July through July). “Per our usual policy, we aren’t making any predictions on adoption for Windows 8 before it hits the market,” the spokesperson added.