As part of its quarterly and annual financial results released late last week, Microsoft announced that it had sold more than 175 million copies of Windows 7 through the third week of July. That milestone comes less than a month after the company's previous Windows 7 sales announcement, when the company revealed that 150 million units had been sold.

"With 175 million licenses sold to date, Windows 7 is the fastest-selling operating system ever and now runs on over 16 percent of all PCs worldwide," Microsoft COO Peter Klein said in a discussion with financial analysts. That means that Microsoft's new OS has an installed base several times larger than that of Windows' closest competitor, Apple's Mac. And it's only been available in the market for nine months.

According to Microsoft, Windows 7 is now selling at a rate of about 10 units every second. Put another way, Microsoft sells almost 1 million copies of Windows 7 every single day. (The company reported 25 million unit sales in the previous 25 days, for example.)

Many have tried to downplay Windows 7 sales statistics simply because Windows is bundled with new PCs. And since PC sales are exploding, Windows 7 is riding that wave, they say. That may be the wrong way to look at this situation. Rather, PC sales are taking off in part because Windows 7 is so good. According to Net Applications, which tracks OS usage via the web, Windows 7 has achieved 14.4 percent usage share on the web in nine months. It took Windows Vista 22 months to reach that point. (StatCounter reports that Windows 7's global usage share is even higher, at 17.6 percent.)

You need only to look at Microsoft's financial statements to understand the impact of this success, however. The company reported record quarterly revenues of $16 billion for the quarter ending June 30. And over a quarter of those revenues, or $4.55 billion, were attributed to the Windows division. That figure represents $1 billion in growth, year over year. (And one year ago, the software giant reported its first-ever annual sales decline in company history.)

Many had speculated that Apple would earn more revenues than did Microsoft in the previous quarter, based in part on the fact that the company had surpassed Microsoft's market cap earlier in the year. That didn't happen—Microsoft's record $16 billion in revenues outpaced Apple's record $15.7 billion—and Microsoft also earned significantly more profits than did Apple: $5.93 billion for Microsoft versus $3.25 billion for Apple. Microsoft has also wrestled the market-cap mantle back from Apple this month, though few bothered to report on that. (The companies have switched positions a few times over the past two weeks.)

Looking ahead, Microsoft is on track to sell 250 million copies of Windows 7 in its first year on the market and well over 300 million copies of the OS in calendar year 2010.