Difference between CMM and CMMi

CMM is a reference model of matured practices in a specified discipline for e.g. Systems Engineering CMM, Software CMM, People CMM, Software Acquisition CMM etc. But they were difficult to integrate as and when needed. So the CMMI evolved as a more matured set of guidelines and was built combining the best components of individual disciplines of CMM(Software CMM, People CMM etc). It can be applied to product manufacturing, People management, Software development etc etc. "I" represents integration.