Performance Appraisal is part of PMS where as PMS is very much wider which includes defining KRA's & assigning weightage to them, setting expectation level & evaluating productivity of the projects assigned.
Performance appraisal is limited to the scope of evaluation on the basis of set parameters.
PMS included design of Various Appraisal Form dept wise, target wise, project wise. setting guidelines for eveluation, designing PDP, emphasising on post appraisal activities too. It is continous effort/activity.