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If you are confused by this new term, BitLocker, well, don't worry, because you are not alone. In a nutshell, BitLocker is a new data encryption technology that is built into both the Enterprise and Ultimate versions of Vista, and also Windows Server 'Longhorn' and is Microsoft's response to one of our top customer requests: address the very real threats of data theft or disclosure from lost, stolen or inappropriately decommissioned PC hardware with a tightly integrated solution in the Windows Operating System.
If you want to understand more about BitLocker and its various features and details, here are some resources:
BitLocker Drive Encryption: Technical Overview
BitLocker Drive Encryption: Executive Overview
BitLocker Drive Encryption Step-by-Step Guide