CPM is an activity-oriented deterministic model that deals with various project tasks. It always deals with tasks for which you know the time taken for completion. Hence, you can determine how long the overall process will last before delivering all the deliverables. On the contrary, the PERT, or project evaluation and review technique, is an event-oriented probability model where you will construct a network of tasks based on the events. Most project managers use this tool to manage tasks for which the completion time is unknown.