'[t[1]6502 machine code for the Nintendo Entertaiment System's 2a03 sound chip. NSF stands for Nintendo Sound Format.

A set of tools create .NSF files like '[[PPMCK], '[[NerdTracker] and '[[Famitracker].

NSF file format specs available from Kevin Horton at '[l[http://kevtris.org/nes/nsfspec.txt[CLICK HERE]