Windows 8 launched last Friday, and there was some concern that it wouldn’t immediately sell. Some were content with Windows 7 while others didn’t even know Windows 8 existed. It seems that those fears may have been unfounded as Microsoft CEO Steve Ballmer said the new OS was performing well.

During the company’s BUILD 2012 conference, Ballmer announced that Microsoft has sold through four million Windows 8 upgrades over the weekend. The Next Web says the number comes from individual purchases as well as bulk purchases from retail outlets. The latter may not have been sold just yet, but it shows that retail has some faith in the new operating system.

So how does the launch of Windows 8 stack up to the launch of Mountain Lion earlier this year? Apple sold through three million upgrades in the four days after its launch. A month later at the iPhone 5 event, Apple CEO Tim Cook said that the company sold 7 million copies of the latest version of Mac OS X. It will be interesting to see if Microsoft can match those numbers a month from now.

In all reality, they probably will and then some. Four million Windows 8 upgrades is like a drop in the bucket when compared to the number of upgradable PCs that are out in the wild. Windows is still on more machines than Mac OS X which makes Microsoft’s job of convincing those PC users to upgrade that much harder. The $40 cost of the upgrade may also turn away many potential consumers until they just buy a new PC that comes equipped with Windows 8.

Speaking of new PCs, Ballmer said that new PC sales were also good over the weekend. He quoted Mark Slater, a Category Director at Dixons Retail, who said that sales of Windows 8 laptops during the weekend were 20 percent higher than expected. HP was also quoted as saying that initial sales were looking good.

It’s hard to tell how well Windows 8 will perform beyond the early adopters and launch buzz. The enterprise market has been slow to adopt Windows 7 and many are outright saying they won’t go near Windows 8. Microsoft’s bet on the consumer market may have been a smart move after all.