This policy setting allows you to configure whether BitLocker requires additional authentication each time the computer starts and whether you are using BitLocker with or without a Trusted Platform Module (TPM). This policy setting is applied when you turn on BitLocker.Note: Only one of the additional authentication options can be required at startup otherwise a policy error occurs.If you want to use BitLocker on a computer without a TPM select the "Allow BitLocker without a compatible TPM" check box. In this mode either a password or a USB drive is required for start-up. When using a startup key the key information used to encrypt the drive is stored on the USB drive creating a USB key. When the USB key is inserted the access to the drive is authenticated and the drive is accessible. If the USB key is lost or unavailable or if you have forgotten the password then you will need to use one of the BitLocker recovery options to access the drive.On a computer with a compatible TPM four types of authentication methods can be used at startup to provide added protection for encrypted data. When the computer starts it can use only the TPM for authentication or it can also require insertion of a USB flash drive containing a startup key the entry of a 4-digit to 20-digit personal identification number (PIN) or both.If you enable this policy setting users can configure advanced startup options in the BitLocker setup wizard.If you disable or do not configure this policy setting users can configure only basic options on computers with a TPM.Note: If you want to require the use of a startup PIN and a USB flash drive you must configure BitLocker settings using the command-line tool manage-bde instead of the BitLocker Drive Encryption setup wizard.