It is connected through a SATA cable to usb, (http://www.amazon.com/gp/product/B01440BTS8?keywords=sata%20cable&psc=1&qid=1456575414&ref_=sr_1_3&s=pc&sr=1-3-spons) And once plugged into pi, it will act as a big usb drive

P.S If you attach a SSD like this, Put “usb max current = 1” so it will work properly.