SAP EAM (Enterprise Asset Management) is evolve from SAP PM (Plant Maintenance). SAP PM was introduce started within SAP R/2, R/3. Later in 2005 with the first ERP release into the market PM term has been replaced with EAM.
The SAP PM module is a subset of SAP EAM. SAP PM contains the key Maintenance Planning and Scheduling functionalities to support successful asset or equipment maintenance. And you will find new process within EAM.