The data memory of the PIC18F4550 is volatile. This means that information stored in this memory is lost when the power is switched off. In many cases this is not a problem, but sometimes it's useful that certain data, e.g. configuration data, is saved even when the board is powered down. To this end, the PIC18F4550 contains 256 bytes of non-volatile EEPROM memory besides the volatile data memory. This memory can be used to store non-volatile information.