To use BitLocker Drive Encryption with Trusted Platform Module (TPM) security hardware to protect your operating system drive, your computer must have a compatible BIOS. If BitLocker and the TPM Management snap-in do not appear to work with your TPM security hardware and BIOS, contact your hardware manufacturer for specific configuration and troubleshooting information.
BitLocker can also be used to protect the operating system drive of computers without compatible TPM security hardware. In this case, the user must insert a USB flash drive containing a BitLocker startup key into the computer before starting the computer. To use BitLocker without a TPM, your computer system BIOS must support using USB flash drives during the early startup process.
By default, when you start the BitLocker setup wizard on an operating system drive from Control Panel or Windows Explorer, it checks for a compatible TPM before enabling BitLocker. To use BitLocker on computers without a compatible TPM, you must modify the Require additional authentication at startup Group Policy setting and select the Allow BitLocker without a compatible TPM check box. This allows BitLocker to use key information stored on a USB drive to encrypt the contents of the drive. When the drive is encrypted by using this method, you must insert the USB key every time the computer is started to authenticate that you are permitted to access the contents of the drive.
When you first enable BitLocker and before you encrypt a drive, the setup wizard allows you to test the availability of USB flash drives during startup. If your BIOS does not support the required functionality, you cannot encrypt the drive.
For more information about the system requirements for BitLocker, see BitLocker Drive Encryption: Technical Overview (http://go.microsoft.com/fwlink/?LinkId=140226).