Attached are 2 screens that help answer your questions.
The first one;
> From OS X Finder, displays the Sierra on SSD, and then the Snow Leopard and Windows (from the HDD) as expected
> Pages from the manual; SATA2_0, SATA2_1, SATA2_2, SATA2_3 (CD, SSD, and HD are attached to these)
> Says it's...