Microsoft KB Archive/929830

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You must install BitLocker on the system volume of a computer that is running Windows Vista

Article ID: 929830

Article Last Modified on 10/26/2007


  • Windows Vista Ultimate
  • Windows Vista Enterprise
  • Windows Vista Ultimate 64-bit Edition
  • Windows Vista Enterprise 64-bit Edition

A computer that is running Windows Vista must have at least two volumes for Windows BitLocker Drive Encryption to work: a startup volume and a system volume. Both volumes must use the NTFS file system. You must install BitLocker on the system volume.

The startup volume contains the Windows operating system and its support files. BitLocker encrypts the data on this volume.

The system volume contains the hardware-specific files that are required to load Windows Vista after the BIOS starts the operating system. For BitLocker to work, the following conditions must be true:

  • The system volume must not be encrypted.
  • The system volume must differ from the startup volume.

The system volume should be at least 1.5 gigabytes (GB).

Note BitLocker does not protect the data that is written to the system volume.

BitLocker requires approximately 50 megabytes (MB) of the 1.5 GB on the system volume. The loader and startup utilities use some additional space. The remaining space is set aside for situations that might require temporary files to be stored on the system volume.


For more information about BitLocker, visit the following Microsoft Web sites:

BitLocker Drive Encryption

BitLocker Drive Encryption: Executive Overview

Windows BitLocker Drive Encryption Step-by-Step Guide

Keywords: kbinfo kbtshoot KB929830