An operating system (OS) is a piece of software that, after being first loaded by a boot programme, governs all other application programs in a computer. The application programs request services from the operating system using a specific application programme interface (API). A user interface, such as a graphical user interface (UI) or command-line interface (CLI), allows users to interact with the operating system directly as well (GUI). An operating system is extremely useful for computer applications and software development. Without an operating system, each application would have to develop its own user interface (UI) and all the required code to control the computer's low-level tasks, such as managing disc storage, network connections, and other tasks. This would greatly increase the size of every application and make software development challenging, especially in light of the wide range of underlying hardware options.