Restart files provide a snapshot of the simulation during an analysis and are used to safeguard against system failure, to pause long analyses, and to extend analyses.
Every time a new restart file is created, the previous one is deleted to minimize the impact on disk space requirements.
The number of restart steps in both the filling and packing phase can be edited. The more steps you save, the more up to date the data file will be, but the slower the analysis time, since the solver will need to ouput more data to file.