Build 6003 is not a standard release version that users could buy on a retail disc. Instead, Build 6003 represents Windows Server 2008 (and Windows Vista) machines that have received the or specialized post-SP2 cumulative updates.
A similar phenomenon occurred with its client counterpart, , for the exact same technical reasons. After installing the relevant Server 2008 updates (starting with KB4493471), some Windows Vista SP2 systems began reporting build 6003. windows server 2008 build 6003
(Dedicated standalone hypervisors) Key Infrastructure Capabilities Build 6003 is not a standard release version