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If you're a company that employs a management tool that does things like hardware and software inventory, software and OS deployments, and a myriad of other centralized management pieces, you know that the Windows operating system inventories differently than the major name given to it by Microsoft.
For example, when inventory filters up to the site database from a System Center Configuration Manager client, Windows 8.1 is shown as version 6.3. But, with Microsoft "skipping" Windows 9 and going straight to Windows 10, what version number will be inventoried?
Well, since Windows 9 will never be officially released, there's no reason it has to have a version number. So, for those wanting to keep record, Windows 10 reports in as Windows version 6.4 in inventory for management tools.
Here's the full, updated table of client Operating System names to Version numbers.
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source:windowsitpro