In optical phase-change materials, especially, Ge2Sb2Te5 has widely been used as a heat of rewritable optical storage media. The chalcogenide material shows a good performance in write-erase cyclability and optical contrast: refractive index change between amorphous and crystal state. However, the high-speed switching mechanism has long been not well understood because of the difficulty of the amorphous analysis. In 2004, we gave one solution for the issue. Since then, a number of discussions and critics have raised up on the new model because the amorphous state in the model is not amorphous like. In this review, we want to give a clear solution to understand what is amorphous in chalcogenides and how different is the amorphous from normal glass amorphous.