Research firm Gartner has said that Windows 7 will become the leading operating system (OS) worldwide in the PC installed base this year.

Gartner said that Windows 7 will be running on 42% of PCs in use by the end of 2011, adding that its latest PC OS forecast shows 94% of new PCs will be shipped with Windows 7 this year.

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.

Research director at Gartner Annette Jump said steady improvements in IT budgets in 2010 and 2011 are helping to accelerate the deployment of Windows 7 in enterprise markets in the US and Asia/Pacific, where Windows 7 migrations started in large volume from 4Q 2010.

"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," added Jump.

"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," Jump said.

Meanwhile shipments of Apple iMacs and Mac OS share on new PCs have aslo seen increases in the last 12 months.

Mac OS was shipped on 4% of new PCs worldwide in 2010 compared with 3.3% in 2008, said Gartner.

The research firm forecasts Mac OS to be on 4.5% of PCs in 2011, and grow to 5.2% of new PCs in 2015.

Shipments will grow stronger in mature markets where consumers are buying into the Apple product ecosystem, said Gartner.

"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.

Linux OS is expected to remain niche over the next five years with its share below 2%.

Gartner does not expect Chrome OS, Android or webOS to get any significant market share on PCs in the next few years.