  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 18x18 cm2 and a pad size of 1x1 cm2. 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.
