[EQAditu]

Right-click "My Computer", select "Manage". Click on the Computer Management -> Storage -> Disk Management node. On the top half you will see your logical drives... ignore that. On the bottom half you will see your physical drives. Each physical drive will also show which logical drives it contains. If you have "Disk 0" with C: and D: in it, you have one physical hard drive. If you have a "Disk 0" and "Disk 1", you have two physical hard drives. Of course if you do have a Disk 1, make sure it isn't just a card reader or something. It'll usually say "Basic" and "Online" if a hard drive. The icon is a good giveaway also.

Though technically, if Device Manager doesn't know about more than one drive, neither will this.