I was reading hardware based encryption, and found out that they are basically of 3 types.
1) SED - Encryption/Decryption done by the drive circuitry. Unlocked via Pre boot authentication. Can use TPM for extra safety.
2) Enclosed FDE - Has a separate chassis, which holds the chip for encryption and decryption. The hdd is inserted in that chassis. Everything going and coming of that disk is encrypted/decrypted on the fly.
3) Bridge and Chipset FDE - This encryptor is put in between the motherboard and the hdd. Their are (mostly) cables for in-out data connections.
What I am confused about, and something that I did not find anywhere is, how is the authentication or the steps are for the 2nd and the 3rd type. Who stores the keys, how does the user sets an authentication type, and who authenticates. Is the process pre-boot too?