Virtual machines need an operating system with which to run, and the operating system most frequently being used in the current wave of virtualization is Windows, according to a survey sponsored by Sage Research and published in its recent Sage/CMB market Pulse newsletter.

Sage Research is the technology practice branch of custom market research firm Chadwick Martin Bailey. Sage surveyed Chadwick Martin Bailey's panel of technology service providers and panel of professional technology users and found 96% of the respondents use Windows on their virtual servers.

Many sites use more than one brand of operating system to run virtual machines. The runner-up was Linux, with 52% of the respondents using the open source operating system. Unix was third at 30% and Solaris fourth at 29%. The figures do not add up to 100% because sites in some cases are using multiple brands of operating system in their virtual machines.

The Mac OS was used by 12% of respondents and NetWare by 6%.

The findings were a broad brush stroke picture of server virtualization. They did not specify how many virtual machines of each kind was running on the virtualized servers or who the virtualization software supplier was.

But the results may indicate that Microsoft, even if it's late in getting its Hyper-V hypervisor to market, still stands to gain from the marketplace's rush to virtualization. Microsoft will launch Windows Server 2008 in February and will make Hyper-V available within six months of that launch date. It plans to offer it both as an option in the operating system or as a standalone product.

Virtualization appears likely to multiply the number of Windows copies being run. Microsoft charges a license fee for a virtual machine operating system, the same as a physical one.

The survey results were based on answers from 126 IT decision makers at companies that have implemented server virtualization and have more than 1,000 employees, Sage said.