On the Microsoft Windows operating system, a process that interacts with the user "must" accept and react to incoming messages, which is almost inevitably done by a message loop in that process. In Windows, a message is equated to an event created and imposed upon the operating system. An event can be user interaction, network traffic, system processing, timer activity, inter-process communication, among others. For non-interactive, I/O only events, Windows has I/O completion ports. I/O completion port loops run separately from the Message loop, and do not interact with the Message loop out of the box.