To date, the Enterprise version of Windows has only been made available to customers of Microsoft's Software Assurance volume licensing program. But today, the software giant confirmed that it will end that limitation and make Windows Enterprise available to others as well.

News of this new standalone version of Windows Enterprise comes courtesy of Mary Jo Foley of All About Microsoft.

As a quick backgrounder, there are currently four mainstream product editions of the current Windows version: Windows 8.1 ("Core"), Windows 8.1 Pro, Windows 8.1 Enterprise and Windows RT 8.1. The first two are available with new PCs and in Full retail packaging. Enterprise was until now available only as part of an SA subscription. And Windows RT 8.1 comes only on new ARM-based Windows devices like Surface 2.

The differences between Windows 8.1 Pro and Enterprise may seem subtle, but they're important, especially since Microsoft no longer offers an "Ultimate" SKU that combines all of the available Windows features into a single package for individuals. Enterprise is (mostly) a super-set of Pro, adding Windows To Go (and the Windows To Go Creator utility), support for AppLocker, BranchCache and DirectAccess, some VDI enhancements, and other features.

(One thing you can't do is add Media Center to Windows 8.x Enterprise.)

According to Microsoft, it is making Windows Enterprise available to non-SA customers as a standalone upgrade SKU in the Open and Select/Select Plus programs beginning March 1, 2014.

"This is a technical change to enable Windows Enterprise to be sold standalone with minimal impact to existing customers," a Microsoft statement notes. "This change expands the availability of the Enterprise edition to now include [other] customers."

It's not clear to me if this means we'll ever see a standalone Enterprise SKU at retail or the ability to upgrade to Enterprise through the "Add Features to Windows 8.1" interface that's available in the product today. (Which you can use to upgrade from Core to Pro or to Pro + Media Center.)