As a part of their Genuine Software Initiative, Microsoft has designed a new method of activation for volume license customers. All editions of Windows Vista and Windows Server 2008 now require activation.
Under this new requirement, there are two types of volume activation 2.0 options for license enrollment:
Key Management Service: a local activation service that is hosted locally in the customer’s environment and managed by the customer/IT department.
Multiple Activation Key: a one-time activation with Microsoft’s hosted activation services. There are a predetermined number of allowed activations dependent upon the volume license agreement that the customer has. Note: Each activation counts towards the predetermined activation limit.
It is possible to use a combination of activation methods within a single enterprise based on the multiple layers within the organization and the network infrastructure. Just be aware of how licensing is counted for each of the activation options.