A method of manufacturing an electronic circuit comprises: providing an electronic circuit having a first configuration in which the circuit comprises a resistive element having a first resistance, and irradiating at least a part of the resistive element with electromagnetic radiation to change the resistance of the resistive element from the first resistance to a second resistance, the second resistance being lower than the first resistance. A method of storing data comprises: receiving a piece of data to be stored; determining a number according to the data; and irradiating at least part of a resistive element with that number of pulses of electromagnetic radiation to change a resistance of the resistive element from a first resistance to a second resistance, the second resistance being lower than the first resistance. A difference between the first resistance and the second resistance is dependent on the number. Corresponding circuits and data storage systems are disclosed.