No. 27 (00109) Family name : Loizides Given name : Constantin Affiliation : Inst. f. Kernphysik, Uni. Frankfurt Abbreviation : IKF E-mail address : loizides@ikf.uni-frankfurt.de Title : Realtime Analysis for the ALICE High Level Trigger Authors : V. Lindenstruth, C. Loizides, D. Roehrich, B. Skaali, T. Steinbeck, R. Stock, H. Tilsner, K. Ullaland, A. Vestbo and T. Vik for the ALICE Collaboration Abstract : The central detectors of the ALICE experiment at LHC will produce a foreseen data size of up to 75 MByte/event at an event rate <200 Hz resulting in a rate of ~15 GByte/sec. This exceeds the foreseen mass storage bandwidth of 1.25 GByte/sec by a factor of 15. Online processing of the data is necessary in order to select interesting (sub)events, or to compress data efficiently by modeling techniques. Processing the data requires a massive parallel computing system, the HLT system located in the data flow after the front-end electronics of the detectors. The system will consist of a farm of clustered SMP-nodes based on off-the-shelf PCs connected with a high bandwidth low latency network. The system nodes will be interfaced to the front-end electronics via optical fibers connecting to their internal PCI-bus, using a custom PCI Receiver Card. These boards provide a FPGA co-processor for data intensive repetetive task of the pattern recognition. Most of the local pattern recognition will be done using the FPGA co-processor while the data is being transferred to the memory of the corresponding nodes. Algorithms for conventional cluster finding and local track finding based on a Circle Hough Transformation of the raw data are currently under development. Tests on prototypes are being done, using both the foreseen software for online data analysis and communication. Latest results concerning the hardware and software implementation will be shown.