A process is a self-contained program which has all the required elements for it to be run on a processor. It is unlikely that it will be able to run on its own, and this requires the help of other processes to provide it with data, or to take data from it. It must thus have some form of communication device to signal its intentions to other processes (and vice-versa). The requirement for many processes to run, at a time, results in the need for a scheduler, which must try and be as fair as possible to all the processes, but which has the main aim of keeping the system running as smoothly as possible, without any system crashes.