Updated: July 9, 2020 (December 4, 2006)

  Charts & Illustrations

BitLocker Volumes Schematic

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Michael Cherry by
Michael Cherry

Michael analyzed and wrote about Microsoft's operating systems, including the Windows client OS, as well as compliance and governance. Michael... more

Partitioning a computer’s hard drive to create the necessary volumes for BitLocker can be complicated. Because few computers purchased without BitLocker preinstalled will have the necessary separate system volume already created, administrators must repartition computer hard drives before configuring BitLocker. Typically, a computer’s hard drive is partitioned with one large volume, with a second smaller volume that contains some OEM-installed maintenance files. In the example shown at the top, the OS volume is the only usable volume, which is labeled as the C drive. In computers without BitLocker, this is the active volume: the computer boots from this volume.

Before BitLocker can be configured, the drive must be repartitioned to create a second system volume, the BitLocker System volume, of at least 1.5GB, as shown in the example at the bottom. The OS volume will still contain the OS files, including the paging and hibernation files. This volume can be encrypted by BitLocker.

The files initially used to boot the OS with BitLocker are moved to the new BitLocker System volume, which is then marked as the active volume. This system volume, with the boot files, cannot be encrypted by BitLocker or by the Encrypting File System (EFS). However, computers with a Trusted Platform Module will be able to determine whether this volume has been tampered with.

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