SAP-HR is with the basic modules of PA,OM,Time Payroll.
SAP-HCM i.e Human Capital Management comes with New Modules like E-recruitment,E-learning, Talent acqusition, Performance workflow.
HCM is basically the New version of SAP-HR.
The main difference is SAP HR is a completely SAP module where as SAP HCM is a Business Suite. SAP HR can be developed and customized by ABAP Codes where HCM can be developed by web based tool.
The SAP HR module was termed as HCM from version 5.0 after the web portal sub modules like e-learning/ e-recruitment , Global & Concurrent Employment, ESS and MSS was build on Netweaver.
The SAP HR module was termed as HCM from version 5.0 after the web portal sub modules like e-learning/ e-recruitment , Global & Concurrent Employment, ESS and MSS was build on Netweaver.
In general terms HR & HCM both are same. HCM is basically the new version of SAP HR.