The ATLAS Pixel Detector provides a very high granularity, high precision set of measurements as close to the interaction point as possible. The system provides three precision measurements over the full acceptance, and mostly determines the impact parameter resolution and the ability of the Inner Detector to find short lived particles such as B-Hadrons. The system consists of three barrels at average radii of ~ 5 cm, 9 cm, and 12 cm (1456 modules), and three disks on each side, between radii of 9 and 15 cm (288 modules). Each module is 62.4 mm long and 21.4 mm wide, with 46080 pixel elements read out by 16 chips, each serving an array of 18 by 160 pixels. The 80 million pixels cover an area of 1.7 m^2. The readout chips must withstand over 300 kGy of ionising radiation and over 5x10^14 neutrons per cm^2 over ten years of operation. The modules are overlapped on the support structure to give hermetic coverage. The thickness of each layer is expected to be about 2.5% of a radiation length at normal incidence. Typically three pixel layers are crossed by each track.
The pixel detector can be installed independently of the other components of the ID. In the starting phase, only two of the three layers planned for will be installed.