"Master" and "Slave" drives:
Don't forget to change the pin connections (with the supplied plug) on your second HDD, (have a peek at the pin connection diagram), to make your 2nd HDD the "Slave" drive.
"Windows" should be on your "Master" Drive
In the Bios Boot sequence the HDD's will appear at two separate, identified, drives...

...!
Paul.... 8-)...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.