The CD-ROM drive is a standard 5.25 IDE and it is being powered externally.
The internal HD in the Amiga is the factory 176Mb which came with the A1200HD back in 1995 (Or something like that, Its Amiga Technologies not Commodore).
There is no buffered IDE as far as i know. I cannot give any more info right now as i am at work, but I'll take a look when i get home and post.