Gartner Research believes that Microsoft's Windows 7 Operating System will be running on 42% of all PCs by the end of 2011. Supporting this move is the fact that 94% of all new PCs shipped in 2011 had Windows 7 pre-installed.

Another interesting note is that "Gartner's forecast assumes that Windows 7 is likely to be the last version of Microsoft OS that gets deployed to everybody through big corporatewide migration."

For Mac OS fans, Gartner believes 4.5% of new PCs shipped in 2011 will run Apple's operating system and that this will rise to 5.4% by 2015.

And for those wondering about Chrome OS or WebOS as desktop operating systems, Gartner says "Gartner does not expect Chrome OS, Android or webOS to get any significant market share on PCs in the next few years."

Their press release :

Gartner Says Windows 7 Will Be Running on 42 Percent of PCs in Use Worldwide By the End of 2011

Improvements in IT Budgets Are Accelerating Windows 7 Deployments in Enterprise Markets in U.S. and Asia/Pacific

STAMFORD, Conn., August 9, 2011— 

Windows 7 will become the leading operating system (OS) worldwide in the PC installed base, running on 42 percent of PCs in use by the end of 2011, according to Gartner, Inc. Gartner's latest PC OS forecast shows 94 percent of new PCs will be shipped with Windows 7 in 2011.

"Steady improvements in IT budgets in 2010 and 2011 are helping to accelerate the deployment of Windows 7 in enterprise markets in the U.S. and Asia/Pacific, where Windows 7 migrations started in large volume from 4Q10," said Annette Jump, research director at Gartner. "However, the economic uncertainties in Western Europe, political instability in selected Middle East and Africa (MEA) countries and the economic slowdown in Japan after the earthquake and tsunami in March 2011 will likely lead to slightly late and slow deployment for Windows 7 across those regions."

Gartner's forecast assumes that Windows 7 is likely to be the last version of Microsoft OS that gets deployed to everybody through big corporatewide migration. In the future, many organizations will also use alternative client computing architectures for standard PCs with Windows OS, and move toward virtualization and cloud computing in the next five years.

"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," Ms. Jump said.

Shipments of Apple iMacs and Mac OS share on new PCs have seen increases in the last 12 months. Mac OS was shipped on 4 percent of new PCs worldwide in 2010 versus 3.3 percent in 2008. Mac OS is forecast to be on 4.5 percent of PCs in 2011, and grow to 5.2 percent of new PCs in 2015. Shipments will grow stronger in mature markets where consumers are buying into the Apple product ecosystem.

"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," Ms. Jump said.

The Mac OS share still varies greatly by region, as Apple has much stronger presence in North America and Western Europe. The fastest growth is expected to happen in selected emerging countries, where Apple and Mac OS are growing from a small base.

Linux OS is expected to remain niche over the next five years with its share below 2 percent because of the remaining high costs of application migration from Windows to Linux. In the consumer market, Linux will be run on less than 1 percent of PCs, as Linux's success with mini-notebooks was short-lived and few mini-notebooks are preloaded with it today.

Gartner does not expect Chrome OS, Android or webOS to get any significant market share on PCs in the next few years. Analysts believe that to get any consideration as an alternative for a traditional PC, lighter OSs will first need to get strong positions on emerging client devices such as Web books and media tablets. Even then, it is unlikely that they will have any impact on Microsoft and Windows OS's hold on positions on traditional professional PCs in the time frame of the current forecast. This is because of application compatibility issues and the high proportion of Windows-specific applications within many enterprises.

Gartner estimates that only in 2012 will the market reach the point of crossover between Windows-specific and OS-agnostic applications for enterprises, as 50 percent of the applications will be OS-agnostic. In the consumer space, Gartner believes that the proportion of OS-agnostic applications is already above the Windows-specific applications. This could help Chrome OS and Android make inroads into the consumer space in the next three to five years.

Additional information is available in the Gartner report "Forecast Analysis: PC OS Market, Worldwide, 2008-2015, 2011 Update" at http://www.gartner.com/resId=1745026.