Microsoft’s OS is estimated to account for about 42 percent of active operating system share this year, while 94 percent of all PCs shipped this year will come with Windows 7 pre-installed.

“By the end of 2011, nearly 635 million new PCs worldwide are expected to be shipped with Windows 7. Many enterprises have been planning their deployment of Windows 7 for the last 12 to 18 months, and are now moving rapidly to Windows 7,” said Annette Jump, research director at Gartner.

According to Gartner, Mac OS X is gaining share and is slowly chipping away at Microsoft. Gartner said that Mac OS was shipped on 4 percent of new PCs worldwide in 2010 versus 3.3 percent in 2008. Mac OS X is forecast to be on 4.5 percent of PCs in 2011, and grow to 5.2 percent of new PCs in 2015.

“The adoption of Mac PCs and Mac OS is a result of Apple’s ability to grow well above the market average in the last 12 to 24 months, thanks to its ease of use from the user interface (UI) point of view and ease of integration with other Apple devices, such as the iPhone, iPad, iPod touch and the existing Apple ecosystem of applications and programs,” Jump said.