  We have updated the parton and hadron cascade model PACIAE for the
relativistic nuclear collisions, from based on JETSET 6.4 and PYTHIA 5.7 to
based on PYTHIA 6.4, and renamed as PACIAE 2.0. The main physics concerning the
stages of the parton initiation, parton rescattering, hadronization, and hadron
rescattering were discussed. The structures of the programs were briefly
explained. In addition, some calculated examples were compared with the
experimental data. It turns out that this model (program) works well.
