Disk encryption

Ok, didn't think that through then, thanks for the explanation. So... this sounds like something that would have been a necessary thing in the Sandy Bridge era where it was possible to have really slow IO buses like USB storage attached to USB 2 buses with encrypted media. The Core 2 I5 2xxx series had AES-NI but some of the motherboards it ended up on didn't have USB 3 controllers so the CPU would be going into idle state because the IO bus was so slow. Am I in the right mental model?