All electronics must exist in an environment of electromagnetic noise from the outside world. EMC is when a device is compatible with its operating environment. A device must be able to cope with EMI from outside sources, and at the same time stay within well defined limits for generating its own EMI within its circuit and to the outside world. EMS is how sensitive a device is to outside sources of EMI. Devices must be able to cope with two types of EMI: radiated EMI and conducted EMI.