Gartner estimated in April that the installed base of Linux PCs will grow this year by 16% to 19.4 million worldwide. In contrast, the installed base of Windows desktops will grow more slowly but on a much bigger base: a projected 11.4% year over year to 1.05 billion PCs. Of that number, 311 million are Vista. Apple ( AAPL) is doing a little better: Macs with the Apple operating system will grow by 11.6% to 28.2 million.

While total installed OS-equipped PCs are expected to grow at 11.8% in 2009, Gartner sees Linux PCs growing by just 10% to 21.4 million, vs. 11.7% for Windows to 1.18 billion. Mac OSs are projected to grow by 17.1% next year to 33 million.

"We are starting to see a lot of interest from very sizeable customers" in the emerging markets of India and China for a viable alternative to Windows on the desktop, John Dunderdale, IBM vice president of sales for Lotus, said in an interview.

"We fore see a huge uptake in the mid-market to running Linux" based on the work IBM is doing with its partners, says Kuznetsova.

Among server operating systems, adoption of Linux by the mid-market, which includes small businesses, has lagged large business use because of the higher level of IT support Linux requires, Kuznetsova says. The perceived complexity and support needs have held back adoption, she adds.

IBM's answer is to do some of the integration work or provide its reseller partners with newly announced toolkits that make it easy for them to bundle and preconfigure Linux software and hardware.

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