Windows was the most popular operating system for new servers in the past three months, for the first time, according to IDC.

Sales of Windows systems accounted for 36.9 percent of all server revenue, against 31.7 percent for Unix and 11.5 percent for Linux, according to IDC analyst Matt Eastwood. Enterprises increasingly are using Windows-based servers for applications such as ERP as well as e-mail and Web hosting. Migration from Windows NT to newer versions of Windows is also driving sales, he said.

The overall worldwide server market grew by 8.1 percent - faster than the predicted six percent.

After a long period focused on cutting costs and buying servers just to run current applications, enterprises are once again investing strategically in systems to handle future workloads, said Eastwood. IT companies are once again being asked to support real growth.

Also Tuesday, Gartner Inc. reported that worldwide server revenue grew 5.6 percent during the third quarter. Gains in sales of servers costing less than US$25,000 led the upward trend, according to both research companies.

"For the first time, you could say that Microsoft has its own legacy, and that legacy is NT," Eastwood said. How much of Windows' gain will be permanent is hard to say, he added. However, just two years ago, Windows servers were only 31.5 percent of the market.

IBM remained the top vendor in revenue terms, with a gain of 10.3 percent to more than $4 billion, while HP stayed in second place as its revenue grew 12.4 percent to reach nearly $3.5 billion. IBM had 32.3 percent of the market versus HP's 27.8, but both gained share. Overall, just under $12.5 billion worth of servers were sold in the quarter, according to IDC.

Processors with 64-bit capability have leapt to the forefront of the x86 server market. In the third quarter, 69 percent of all x86 servers sold had 64-bit-capable processors, compared with just nine percent a year earlier. Most of those chips are still running only 32-bit applications, but enterprises are investing for the future, Eastwood said.