The crystallization processes of the Ge2Sb2Te5 thin film used for PD and DVD-RAM were studied in its realistic optical disk film configurations for the first time by X-ray diffraction using an intense X-ray beam of a synchrotron orbital radiation facility (SPring-8) and in situ quick detection with a Position-Sensitive-Proportional-Counter. The dependence of the amorphous-to-fcc phase-change temperature T-1 on the rate of temperature elevation R-et gave an activation energy E-a: 0.93 eV much less than previously reported 2.2 eV obtained from a model sample 25-45 times thicker than in the real optical disks. The similar measurement on the Ge4Sb1Te5 film whose large reflectance change attains the readability by CD-ROM drives gave E-a: 1.13 eV with larger T, than Ge2Sb2Te5 thin films at any R-et implying a lower sensitivity in erasing as well as a better data stability of the phase-change disk. (c) 2004 Elsevier B.V. All rights reserved.