To turn on BitLocker Drive Encryption on an operating system drive
1.Click Start, click Control Panel, click System and Security, and then click BitLocker Drive Encryption.
2.Click Turn On BitLocker for the operating system drive. BitLocker will scan your computer to make sure that it meets the BitLocker system requirements. If your computer meets the requirements, BitLocker will inform you of the next steps that need to be taken to turn on BitLocker, such as drive preparation, turning on the TPM, and encrypting the drive.
If your TPM is not initialized, the BitLocker setup wizard will instruct you to remove any CDs, DVDs, or USB drives from the computer and restart the computer to begin the process of turning on the TPM. You will either be prompted to enable the TPM before the operating system boots or in some cases you will need to navigate to the BIOS options and enable the TPM manually. This behavior depends on the BIOS of the computer. After you confirm that you want the TPM enabled, the operating system will start and the Initializing the TPM security hardware progress indicator will be displayed.
One of the items that BitLocker checks is the configuration of the system partition. BitLocker requires a minimum system partition size of 100 MB. However, if you have a system partition size between 101 MB and 299 MB, an error message will be displayed about the Windows Recovery Environment. You may disregard this message and continue with BitLocker setup.
If you encrypt your hard drive with BitLocker drive encryption, the System Reserved partition contains the necessary files for starting your computer. Your computer boots the unencrypted System Reserved partition, and it will decrypt the main encrypted drive and boot the encrypted Windows system.