Critical Path Analysis

Critical Path Analysis (CPA), also known as the Critical Path Method (CPM), is a project scheduling technique used to identify the sequence of tasks that determines the minimum duration of a project. The "critical path" is the longest path through the network of tasks, and therefore the one least tolerant of slippage — any delay on the critical path directly delays the project as a whole.

The technique was developed in 1956 by James E. Kelley Jr. (of Remington Rand) and Morgan R. Walker (of DuPont), building on scheduling work done at DuPont during the Manhattan Project. It was first trialled on plant shutdowns in 1957, and the first paper on critical path scheduling was published in 1959.

Critical Path Analysis works by algorithmically analyzing the complete set of activities required to complete a project, along with their durations, inter-dependencies, and end-points such as deliverables. This can be applied not only to the final project end-date, but to any intermediate milestone or deliverable within the project.

The calculations involved, though conceptually straightforward, are often large in number, and the development of CPA was closely tied to the emergence of computing technology — it was one of the major applications of early computers. Originally implemented on complex mainframe systems that took operators many months to learn, CPA tools migrated to minicomputers in the 1970s and 1980s (still expensive and restricted to large organisations), before becoming widely accessible with the rise of microcomputers during the 1980s.

[PERT charts], developed in 1958, built directly on Critical Path Analysis, extending the technique with probabilistic time estimates to better handle scheduling uncertainty.