Dr. Michael Pound, a computer science researcher and professor at the University of Nottingham, uses hashcat and 4 GPUs in parallel to go through 1o billion hashes a second in this Computerphile video. He calls his deep-learning server the "Beast." If you're new to cracking passwords, he does a great job breaking down the process of what's going on as hashcat does its magic.

Source : http://null-byte.wonderhowto.com/news/beast-cracks-billions-passwords-seconds-0172287/