Systems and methods for preventing the unauthorized access to data stored on removable media, such as software, include storing a predetermined signature in the area of non-volatile memory in a computer system. In general, the cumulative delay of the delay line defines a window in time having its zero point anchored to the beginning of the delay line. The infrared source is cooled by pressurized air passing through an interior portion of the removable air bar channel assembly, and the air is further conducted into fluid contact with the web in an air gap between the emitter and web to promote convective heat transfer and to contribute to the air pressure field supporting web flotation.