ALICE HLT high speed tracking and vertexing

The on-line event reconstruction in ALICE is performed by the High Level Trigger, which should process up to 2000 events per second in proton-proton collisions and up to 200 central events per second in heavy-ion collisions, corresponding to an input data stream of 30 GB/s. In order to fulfil the time requirements, a fast on-line tracker has been developed which can optionally use GPU hardware accelerators. The algorithm combines a Cellular Automaton method being used for a fast pattern recognition and the Kalman Filter method for fit of found trajectories and for the final track selection. A fast estimate of the vertex position is based on measurements from the Silicon Pixel Detector. The vertexer is used for the on line monitoring of the ALICE interaction point.