Windows Slideshow: Windows 7 RC Features Many Small but Useful Enhancements
The release candidate of Windows 7 (Build 7100) features many small enhancements over the beta released last January. The new operating system's security features and the Aero Glass interface have undergone much tweaking and tuning. The biggest late-arriving feature to the OS—the virtualization-based Windows XP Mode—remains missing; that code will be available separately via download at a later time.
From slide #15:
BitLocker Without TPM BitLocker, Windows 7's built-in full-disk encryption tool, wants to write the encryption keys to the computer's TPM chip. If no TPM is present, users need to change some group policy settings so they can write the key to a USB stick.