Process chain

Hi experts ,there are many BPC DM packages that run daily in the night .All are using same process chain . If DM package gets triggered at scheduled time while other package is running , package that is already running is getting canceled after some time The later one is getting completed with no issues .

Is it that because same process chain is used in all of the packages ? How process chain works ? Instance of process chain gets created for each DM package?

Thanks in advance.