Windows Enterprise

Microsoft said users of Windows 7 Enterprise and 8/8.1 Enterprise will not be eligible for a free upgrade.

But Microsoft said its Active Software Assurance (ASA) customers -- which typically buy enterprise licenses -- can upgrade to Windows 10 outside of the free program. However, some partners don't view ASA as a free upgrade path because the program costs money. Typically, an ASA license costs an additional 80 percent on top of the base OS licensing fee.

To make matters more confusing, in order for a partner to hold a Windows 7, 8 or 8.1 Enterprise license, it needs to be an ASA paying customer.

"In typical fashion, consumers get a free pass with Windows 10 and Microsoft enterprise customers end up paying more," said Paul DeGroot, principal analyst at Pica Communications, a Microsoft licensing consultancy in Camano Island, Wash.