  The Multi-conjugate Adaptive Optics RelaY (MAORY) should provide 30% SR in K
band (50% goal) on half of the sky at the South Galactic Pole. Assessing its
performance and the sensitivity to parameter variations during the design phase
is a fundamental step for the engineering of such a complex system. This step,
centered on numerical simulations, is the connection between the performance
requirements and the Adaptive Optics system configuration. In this work we
present MAORY configuration and performance and we justify theAdaptive Optics
system design choices.
