Functional requirements refer to how a piece of a system functions or what it does given specific inputs. Nonfunctional requirements (NFRs) refer to such business and engineering needs as performance, reliability, availability, stability, usability, compatibility with interfaces, and security. They are crucial inputs for architects and system designers when performing such tasks as specifying information flows, defining deployment scenarios, choosing software platforms, sizing system configurations, determining required levels of redundancy, and identifying system measurement instrumentation. NFRs that have been clearly and succinctly written contribute to the success of a project by reducing the time required to understand them and to devise and implement procedures for ensuring and verifying that they have been met. By contrast, poorly written NFRs can lead to confusion among developers and architects, resulting in much wasted time, or to the failure and cancellation of a project, especially if the delivered system crashes often or runs too slowly.