What is RCM and what the deference between RCM and PM?

RCM is the a methodology for choosing right PM jobs for the equipments. RCM takes a system level approach and analyzes the effects of all failure modes on system level. RCM scrutinizes PM activities on effective and applicable parameters. Effective means it makes something better to equipments and applicable means its cost benefit analysis. if the PM is expensive than run to failure then RCM recommends for run to failure. 

RCM is way of analyzing and selecting the effective and applicable PM activities.