Before you can turn on BitLocker Drive Encryption you need to make sure that your computer's hard disk has at least two volumes. If you create a new volume after you have already installed Windows, you will have to reinstall Windows before turning on BitLocker.

One volume is for the operating system drive (typically drive C) that BitLocker will encrypt, and one is for the active volume, which must remain unencrypted to start the computer. The size of the active volume must be at least 1.5 gigabytes (GB). Both partitions must be formatted with the NTFS file system. You can also encrypt data drives on the same computer, but the drive that Windows is installed on must also be encrypted with BitLocker.


  • The terms partition and volume are often used interchangeably. On most computers, they are the same: one partition equals one volume. On larger computer systems, however, it is possible to have a single volume span several partitions. BitLocker installs on a simple volume, where one volume equals one partition.

If you do not already have two partitions, you can use the BitLocker Drive Preparation Tool to help get your system ready for BitLocker by creating the required second partition.

If you are using Windows Vista Ultimate, you can download and install the BitLocker Drive Preparation Tool from Ultimate Extras. Download and install the Ultimate Extra called BitLocker and EFS enhancements. After you have installed this tool, type BitLocker into the Start menu search box, and then double-click BitLocker Drive Preparation Tool to run the tool. After the tool runs, you must restart your computer before turning on BitLocker.

If you are using Windows Vista Enterprise, you can get the BitLocker Drive Preparation Tool through these standard support channels:

For additional information about the BitLocker Drive Preparation Tool, see this Knowledge Base article on the Microsoft Help and Support website.


If your computer meets these requirements, you can turn on BitLocker.

To turn on BitLocker

  1. Open Bitlocker Drive Encryption by clicking the Start button Picture of the Start button, clicking Control Panel, clicking Security, and then clicking Bitlocker Drive Encryption. Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

  2. Click Turn on BitLocker.

  3. Follow the instructions in the BitLocker Setup wizard.