The M90 uses ARRI's MAX Technology, a reflector design that combines some of the advantages of a PAR and a Fresnel. Unlike a traditional PAR, there are no spread lenses to swap. You simply turn a focus knob and adjust the beam from roughly 15°–49°.
The fixture runs either a 9,000W HMI lamp, or a 6,000W HMI lamp in the same head.
The big selling point is that the M90 produces output approaching a traditional 12K PAR while remaining much closer in size and handling to a 6K fixture. ARRI specifically designed it to fill the gap between the M40 and the ARRIMAX 18/12.