Microsoft is limiting the number of machines to which users can transfer Windows Vista licenses as part of licensing changes the company has made to its Windows client OS.

When Windows Vista is available, consumers will be able to transfer the OS license they purchase to only one machine other than the one for which they originally buy Vista, said Shanen Boettcher, a Windows general manager at Microsoft. He said Microsoft thought the change made sense because "lifetimes for PCs are getting longer." Most likely, a user will not need to transfer an OS license to more than one computer during the time that OS is the latest one available, Boettcher said.

"It's a fit for what most customers do," he said. Boettcher added that XP did not have a specific limit for the number of times the license was transferable, but that Microsoft wanted to be "specific" about transfer rights with Vista.

One Windows user in New York said that one transfer is "probably enough for most people." However the user, who asked not to be named, said the change may encourage Windows piracy among PC enthusiasts who update their machines on a more regular basis. "Power users will pirate what they need," he said.

Another change Microsoft made to Windows client licensing since XP is that only two versions of Vista -- Windows Vista Ultimate and Windows Vista Business -- can be run as a virtual OS in a virtual machine.

"Virtualization is a new technology, and it's primarily used in the business space and by technology enthusiasts," Boettcher said. "It fits in well with the target audience for these [Windows versions]." Windows XP did not have any restrictions on running in a virtual environment, he added.

Microsoft also has tightened up antipiracy features in Vista, and users who do not verify that their version of the OS is authentic with a software license key within 30 days of its activation will lose the use of certain features of the PC until they do so. The company unveiled this characteristic of Vista, called its Software Protection Platform, about two weeks ago.

Joel Richman, a Windows user in Boston, said that as long as the process of checking for pirated software "does not stop my workflow in the middle of the day," he approves of this change to Vista's license. "As a consumer, I wouldn't want a pirated version of [Vista] because I want all the support I expect to go with a licensed piece of software," Richman said.