Answer: Non-functional requirement (NFR) are the requirements that display the attributes of the software system such as usability,maintainability, performance etc. The operations of the operating system is judged by these factors which acts as the standard.
This gives the knowledge about the effectiveness and efficiency of the system after the evaluation of the system on these parameters.If the negative result for the non functional requirement is gained after the evaluation , this indicates the failure of the system.
Example:-throughput of operating system.