The CALICE collaboration is studying the design of high performance electromagnetic and hadronic calorimeters for future International Linear Collider detectors. For the electromagnetic calorimeter, the current baseline choice is a high granularity sampling calorimeter with tungsten as absorber and silicon detectors as sensitive material. A "physics prototype" has been constructed, consisting of thirty sensitive layers, Each layer has an active area of 18 x 18 cm(2) and a pad size of 1 x 1 cm(2). The absorber thickness totals 24 radiation lengths, It has been exposed in 2006 and 2007 to electron and hadron beams at the DESY and CERN beam test facilities, using a wide range of beam energies and incidence angles. In this paper, the prototype and the data acquisition chain are described and a summary of the data taken in the 2006 beam tests is presented. The methods used to subtract the pedestals and calibrate the detector are detailed. The signal-over-noise ratio has been measured at 7.63 +/- 0.01. Some electronics features have been observed; these lead to coherent noise and crosstalk between pads, and also crosstalk between sensitive and passive areas. The performance achieved in terms of uniformity and stability is presented. ; Repond, J. Yu, J. Hawkes, C. M. Mikami, Y. Miller, O. Watson, N. K. Wilson, J. A. Mavromanolakis, G. Thomson, M. A. Ward, D. R. Yan, W. Badaud, F. Boumediene, D. Carloganu, C. Cornat, R. Gay, P. Gris, Ph. Manen, S. Morisseau, F. Royer, L. Blazey, G. C. Chakraborty, D. Dyshkant, A. Francis, K. Hedin, D. Lima, G. Zutshi, V. Hostachy, J. -Y. Morin, L. Garutti, E. Korbel, V. Sefkow, F. Groll, M. Kim, G. Kim, D-W. Lee, K. Lee, S. Kawagoe, K. Tamura, Y. Bowerman, D. A. Dauncey, P. D. Magnan, A. -M. Noronha, C. Yilmaz, H. Zorba, O. Bartsch, V. Butterworth, J. M. Postranecky, M. Warren, M. Wing, M. Giannelli, M. Faucci Green, M. G. Salvatore, F. Wu, T. Bailey, D. Barlow, R. J. Kelly, M. Snow, S. Thompson, R. J. Danilov, M. Kochetkov, V. Baranova, N. Ermolov, P. Karmanov, D. Korolev, M. Merkin, M. Voronin, A. Bouquet, B. Callier, S. Dulucq, F. Fleury, J. Li, H. Martin-Chassard, G. Richard, F. de la Taille, Ch. Poeschl, R. Raux, L. Ruan, M. Seguin-Moreau, N. Wicelk, F. Zhang, Z. Anduze, M. Boudry, V. Brient, J-C. Clerc, C. Gaycken, G. Jauffret, C. Karar, A. de Freitas, P. Mora Musat, G. Reinhard, M. Rouge, A. Sanchez, A. L. Vanel, J-Ch. Videau, H. Zacek, J. Cvach, J. Gallus, P. Havranek, M. Janata, M. Marcisovsky, M. Polak, I. Popule, J. Tomasek, L. Tomasek, M. Ruzicka, P. Sicho, P. Smolik, J. Vrba, V. Zalesak, J. Arestov, Yu. Baird, A. Halsall, R. N. Nam, S. W. Park, I. H. Yang, J. Bundesministerium fur Bildung und Forschung, Germany ; Helm holtz-Nachwuchsgruppen [VH-NG-206]; BMBF [05HS6VH1]; Alexander von Humboldt Foundation [RUS1066839 GSA]; joint Helmholtz Foundation and RFBR [HRJRG-002]; Russian Agency for Atomic Energy, ISTC [3090]; Russian Grants [SS-1329.2008.2, RFBR0402/17307a]; Russian Ministry of Education and Science ; CRI(MST) of MOST/KOSEF in Korea ; US Department of Energy ; US National Science Foundation ; Ministry of Education, Youth and Sports of the Czech Republic [AV0 Z3407391, AV0 Z10100502, LC527]; Grant Agency of the Czech Republic [202/05/0653]; Science and Technology Facilities Council, UK We would like to thank the technicians and the engineers who contributed to the design and construction of the prototypes, including U.Cornett, G.Falley, K.Gadow, P.Gottlicher, S.Karstensen and P.Smirnov. We also gratefully acknowledge the DESY and CERN managements for their support and hospitality, and their accelerator staff for the reliable and efficient beam operation. We would like to thank the HEP group of the University of Tsukuba for the loan of drift chambers for the DESY test beam. The authors would like to thank the RIMST (Zelenograd) group for their help and sensors manufacturing. This work was supported by the Bundesministerium fur Bildung und Forschung, Germany; by the Helm holtz-Nachwuchsgruppen grant VH-NG-206; by the BMBF, grant no. 05HS6VH1; by the Alexander von Humboldt Foundation (Research Award IV, RUS1066839 GSA); by joint Helmholtz Foundation and RFBR grant HRJRG-002, Russian Agency for Atomic Energy, ISTC grant 3090; by Russian Grants SS-1329.2008.2 and RFBR0402/17307a and by the Russian Ministry of Education and Science; by CRI(MST) of MOST/KOSEF in Korea; by the US Department of Energy and the US National Science Foundation; by the Ministry of Education, Youth and Sports of the Czech Republic under the projects AV0 Z3407391, AV0 Z10100502, LC527 and by the Grant Agency of the Czech Republic under the project 202/05/0653; and by the Science and Technology Facilities Council, UK. 17 IOP PUBLISHING LTD BRISTOL 343SR