The 7×7 reconstruction is modeled according to a dimer-adatom-stacking fault (DAS) model constructed by many research groups over a period of 25 years. Extending through the five top layers of the surface, the unit cell of the reconstruction contains 12 adatoms and 2 triangular subunits, 9 dimers, and a deep corner hole that extends to the fourth and fifth layers. This structure was gradually inferred from LEED and RHEED measurements and calculation, and was finally resolved in real space by Gerd Binnig, Heinrich Rohrer, Ch. Gerber and E. Weibel as a demonstration of the STM, which was developed by Binnig and Rohrer at IBM's Zurich Research Laboratory. The full structure with positions of all reconstructed atoms has also been confirmed by massively parallel computation.