I should have clarified, I meant non OS disks
BitLocker does not contain an intentionally built-in backdoor; without a backdoor there is no way for law enforcement to have a guaranteed passage to the data on the user's drives that is provided by Microsoft. The lack of any backdoor has been a concern to the UK Home Office,[22] which tried entering into talks with Microsoft to get one introduced, although Microsoft developer Niels Ferguson and other Microsoft spokesmen state that they will not grant the wish to have one added.
While Biddle denies building in a backdoor, his team worked with the FBI to teach them how they could possibly retrieve data, including targeting the backup encryption keys of users.
"As soon as we said that, the mood in the room changed dramatically," said the anonymous Microsoft engineer to Mashable. "They got really excited."
Bingo. The PIN/password controls access to the actual encryption key, which is typically stored in the TPM (or a USB flash drive). There's an MS blog that goes over all of this, but I can't for the life of me find it at the moment.I understand the question. Seeing as we can change the password instantly we cannot possibly be encrypting the contents of the drive with the password we type in. If we did it would have to re-encrypt the whole drive.
I haven't been able to find a source, but I presume that the user password is used to encrypt the primary encryption key used for the drive. So your user password unlocks the device password which then decrypts the data.
So when you change your user password you just re-encrypt the device password. Seeing as that doesn't change you don't need to encrypt the contents again.