Microsoft yesterday laid out the exclusive features of Windows 8 Enterprise, one of three editions of the upcoming OS and the only one limited to corporate customers.

Windows 8 Enterprise will be available only to businesses that have signed Software Assurance deals with Microsoft. Software Assurance is a kind of software insurance that lets firms upgrade to every new version of a specific product released during the life of the agreement.

Software Assurance fees typically run 23 to 29 percent of a desktop product's license price for each year of coverage.

In a Wednesday blog post, Erwin Visser, a senior director for Windows, outlined the features that will be limited to Windows 8 Enterprise, including the new "Windows to Go," which lets IT administrators burn an image of an in-house PC to a USB thumb drive.

Windows to Go, which Microsoft unveiled last September, will run on PCs or other devices powered by Windows 7 or Windows 8.

Microsoft again touted the feature as a secure way for out-of-office workers to access corporate resources from personal or shared devices, and as a solution to the "bring your own PC" problem of people using their own machines, which may be less secure and more likely to be malware infected, to connect with the company's network.

Last fall, Microsoft declined to say whether Windows to Go was an enterprise-only feature and if it would come at an additional cost.

Yesterday, Visser said that Windows to Go - and several other features he called out - were "available exclusively to Windows 8 Enterprise customers." He also said that what he called "a new companion device license" was necessary if workers brought their own devices into the office for use with Windows to Go.

Microsoft has yet to set the price of that companion device license, according to Paul DeGroot, the founder of Pica Communications, and a well-known expert in deciphering Microsoft's complex, often-obtuse licensing.

Other features found only in Windows 8 Enterprise, Visser said, range from DirectAccess, which lets remote workers access corporate resources without a VPN, or virtual private network, to sideloading of company-built Metro apps, letting administrators control what goes on employees' devices and eliminating the need for them to tap into the consumer-grade Windows Store.

Several of the features Visser referenced, including DirectAccess, AppLocker and BranchCache, are not new but simply updated versions for Windows 8.

Microsoft has also removed the exclusivity label from some features formerly available only in Windows 7 Enterprise, and added them to Windows 8 Pro as well. Top on that list: BitLocker and BitLocker to Go full-disk encryption.

Windows 8 Enterprise is essentially Windows 8 Pro, the most feature-filled of the two retail editions Microsoft will launch later this year, with numerous exclusive features added to the program.