5. System Calls

In any modern operating system, the kernel provides a set of interfaces by which processes running in user-space can interact with the system. These interfaces give applications controlled access to hardware, a mechanism with which to create new processes and communicate with existing ones, and the capability to request other operating system resources. The interfaces act as the messengers between applications and the kernel, with the applications issuing various requests and the kernel fulfilling them (or returning an error). The existence of these interfaces, and the fact that applications are not free to directly do whatever they want, is key to providing a stable system.