At the moment students in the 3/4 area are learning about hardware and software as well as input and output devices. Here is a link that provides students with something to to think about.
http://www.digipubs.vic.edu.au/pubs/digitaltechnologies/digital-technologies-F_L2_digital_systems
http://www.digipubs.vic.edu.au/pubs/digitaltechnologies/digital-technologies-F_L2_digital_systems