BitLocker Drive Encryption
This feature is included in the following editions of Windows Vista:
BitLocker Drive Encryption is a data protection feature available in Windows Enterprise and Ultimate for client computers and in Windows Server 2008. BitLocker is Microsoft's response to a frequent customer request: address these 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.
BitLocker prevents a thief who boots another operating system or runs a software hacking tool from breaking Windows Vista file and system protections or performing offline viewing of the files stored on the protected drive.

BitLocker Drive Encryption for home or office PCs.
The feature ideally uses a Trusted Platform Module (TPM 1.2) to protect user data and to ensure that a PC running Windows Vista has not been tampered with while the system was offline. BitLocker provides both mobile and office enterprise information workers with enhanced data protection should their systems be lost or stolen and secure data deletion when it comes time to decommission those assets.
BitLocker enhances data protection by bringing together two major sub-functions: drive encryption and the integrity checking of early boot components.
Drive encryption protects data by preventing unauthorized users from breaking Windows file and system protection on lost, stolen or inappropriately decommissioned computers. This protection is achieved by encrypting the entire Windows volume; with BitLocker all user and system files are encrypted including the swap and hibernation files.
Integrity checking the early boot components helps to ensure that data decryption is performed only if those components appear unmolested and that the encrypted drive is located in the original computer.
Windows BitLocker is for both business and personal users who need to help protect sensitive data on their PC.
Ready to set up your computer? This paper offers specific guidelines for securing your PC running Windows Vista.