A file with the extension .NSU is a file containing modified system settings created and used by NVIDIA nTUNE.

NVIDIA nTUNE is an application that allows the user to modify system settings i.e bus speeds, fan speeds, CPU voltages, etc. and test them without the need to reboot their system.

Using NVIDIA nTUNE allows the creation of multiple system profiles each saved as a .NSU file, creating the abilty to switch between different preset system profiles for different purposes.