XPS 8930, where and what is the c: drive?

I need to recycle (re: drop off at Goodwill) by wife's 3-1/2 year old 8930.  SHM at that but moving on. I have removed the 1 TB Toshiba HDD but I see no other "drives". I restarted the PC and it came up showing a 220 GB c: drive with the OS. I did see 2 memory cards on the motherboard with 2 additional slots for cards. Below those there is what appears to be another (smaller in size) memory card. 

What is the OS on and where is it located? Any help here is appreciated.