Parametrized simulation of the CMS calorimeter using GFlash

The simulation of the CMS detector operating at the CERN Large Hadron Collider (LHC) is based on the GEANT 4 software package. An alternative simulation of the CMS electromagnetic (ECAL) and hadronic (HCAL) central and forward calorimeters based on the GFlash parameterization package has been implemented into the CMS software structure. The GFlash program is a fast simulation of electromagnetic and hadronic showers using parameterizations of longitudinal and lateral shower profiles. We report on tuning the CMS calorimeter response to ECAL and HCAL test-beam data and compare the gain in CPU time to the standard GEANT 4 calorimeter simulation.