2a03 machine code for the Nintendo Entertaiment System. NSF stands for Nintendo Sound Format. A set of tools create the .nsf files like '[1[http://battleofthebits.com/lyceum/view/PPMCK[PPMCK], '[1[http://battleofthebits.com/lyceum/view/NerdTracker_II[NerdTracker] and Famitracker. NSF file format specs available from Kevin Horton at '[1[http://www.tripoint.org/kevtris/nes/nsf.html[CLICK HERE]