In the words of Boss:

The FZ-5 may be modern pedal built for the modern guitarist, but the sounds you can get from the FZ-5 are pure retro. Looking back at the glorious rock sounds of the 60s and 70s, the FZ-5 recreates its vintage fuzz through BOSS state-of-the-art COSM technology. Recall the fuzz-filled flavors of classic pedals, such as the Maestro FZ-1A, Fuzz Face and Octavia pedals, and kick em into overdrive with the FZ-5s Boost knob.