BitLocker overview

Bitlocker is a Windows disk encryption feature, designed to protect data by providing encryption for entire volumes.
BitLocker addresses the threats of data theft or exposure from lost, stolen, or inappropriately decommissioned devices.

BitLocker provides maximum protection when used with a Trusted Platform Module (TPM). A TPM is a hardware component installed in many devices and it works with BitLocker to help protect user data and to ensure that a computer hasn't been tampered with while the system is offline.

On devices that don't have a TPM, BitLocker can still be used to encrypt the Windows operating system drive. However, this implementation requires the user to insert a USB startup key to start the device or resume from hibernation. An operating system volume password can be used to protect the operating system volume on a computer without TPM. Both options don't provide the pre-startup system integrity verification offered by BitLocker with a TPM.

In addition to the TPM, BitLocker offers the option to lock the normal startup process until the user supplies a personal identification number (PIN) or inserts a removable device (such as a USB flash drive) that contains a startup key. These additional security measures provide multifactor authentication and assurance that the computer won't start or resume from hibernation until the correct PIN or startup key is presented.

Practical applications

Data on a lost or stolen device is vulnerable to unauthorized access, either by running a software-attack tool against it or by transferring the computer's hard drive to a different computer. BitLocker helps mitigate unauthorized data access by enhancing file and system protections. BitLocker also helps render data inaccessible when BitLocker-protected devices are decommissioned or recycled.

System requirements

BitLocker has the following hardware requirements:

  • For BitLocker to use the system integrity check provided by a TPM, the computer must have TPM 1.2 or later versions. If a computer doesn't have a TPM, saving a startup key on a removable drive, such as a USB flash drive, becomes mandatory when enabling BitLocker

  • A device with a TPM must also have a Trusted Computing Group (TCG)-compliant BIOS or UEFI firmware. The BIOS or UEFI firmware establishes a chain of trust for the pre-operating system startup, and it must include support for TCG-specified Static Root of Trust Measurement. A computer without a TPM doesn't require TCG-compliant firmware

  • The system BIOS or UEFI firmware (for TPM and non-TPM computers) must support the USB mass storage device class, including reading small files on a USB flash drive in the pre-operating system environment


    TPM 2.0 is not supported in Legacy and Compatibility Support Module (CSM) modes of the BIOS. Devices with TPM 2.0 must have their BIOS mode configured as native UEFI only. The Legacy and CSM options must be disabled. For added security, enable the secure boot feature.

    Installed Operating System on hardware in Legacy mode stops the OS from booting when the BIOS mode is changed to UEFI. Use the tool MBR2GPT before changing the BIOS mode, which prepares the OS and the disk to support UEFI.

  • The hard disk must be partitioned with at least two drives:

    • The operating system drive (or boot drive) contains the operating system and its support files. It must be formatted with the NTFS file system
    • The system drive contains the files that are needed to load Windows after the firmware has prepared the system hardware. BitLocker isn't enabled on this drive. For BitLocker to work, the system drive must not be encrypted, must differ from the operating system drive, and must be formatted with the FAT32 file system on computers that use UEFI-based firmware or with the NTFS file system on computers that use BIOS firmware. It's recommended that the system drive be approximately 350 MB in size. After BitLocker is turned on, it should have approximately 250 MB of free space


When installed on a new device, Windows automatically creates the partitions that are required for BitLocker.

An encrypted partition can't be marked as active.


When installing the BitLocker optional component on a server, the Enhanced Storage feature also needs to be installed. The Enhanced Storage feature is used to support hardware encrypted drives.

Windows edition and licensing requirements

The following table lists the Windows editions that support BitLocker enablement:

Windows Pro Windows Enterprise Windows Pro Education/SE Windows Education
Yes Yes Yes Yes

BitLocker enablement license entitlements are granted by the following licenses:

Windows Pro/Pro Education/SE Windows Enterprise E3 Windows Enterprise E5 Windows Education A3 Windows Education A5
Yes Yes Yes Yes Yes

For more information about Windows licensing, see Windows licensing overview.