At the beginning of this article we mentioned that a system is characterized by the goals that need to be achieved. In a typical time sharing operating system processes are scheduled so that CPU time is shared among the group. Depending on the scheduling algorithm, each process gets its share amount of CPU time but there is no guarantee that a process gets the CPU whenever it wants to. On the other hand, in a real time system a process is guaranteed to get CPU attention when a specific event happens. There should be an operational deadline from the time the event is triggered to the time the system responds back. Processes in a real time system are mission critical for example in the case of industrial robots in an assembly line where at each stage a certain operation is expected to take place.
In British English, some words from French, Latin or Greek end with a consonant followed by an unstressed -re (pronounced ( non-rhotic accent ) /ə(ɹ)/ or ( rhotic accent ) /ɚ/ ). In American English, most of these words have the ending -er .   The difference is most common for words ending -bre or -tre : British spellings calibre , centre , fibre , goitre , litre , lustre , manoeuvre , meagre , metre , mitre , nitre , ochre , reconnoitre , sabre , saltpetre , sepulchre , sombre , spectre , theatre (see exceptions) and titre all have -er in American spelling.