CPM was developed by the engineers of the Du Pont Company in the 1950s for its application in all scheduling work, construction projects, research and development programmes and in many other situations that require estimates of time and performance. It calls for dividing a programme or project into its elementary parts in their chronological order of sequence. By breaking a project into interconnecting parts, the CPM technique is helpful in finding out the more strategic elements of a plan for the purpose of better designing, planning, coordinating and controlling the entire project.
In a network of activities one can enumerate a number of sequences of operations (paths) from starting event to end event of the project. Each sequence contains different combinations of activities with different durations. The study of the duration of various paths in a project can tell us the minimum time in which a particular project can be completed. The sequence of activities (path) for which the duration is the maximum indicates the minimum duration for the completion of the project.
This path is known as the ‘Critical Path’ being the path of maximum duration and reflects the minimum time necessary for the completion of the project. The critical path is so called because any delay in the completion of the activities lying on this path would cause a delay in the whole project. To finish the project in time, the activities lying on the critical path should be given top priority.