What are Gantt charts and CPM/PERT/?

Simplification

Gantt charts are ideal for straightforward projects with few interlinking tasks. Gantt charts present project tasks and time allocation as the only two pieces of data. While this is a limitation where there are interconnecting tasks that depend on each other, for more basic projects it is easier to interpret the data in a Gantt chart. PERT charts, while also including project tasks and time allocation, display dependency. Gantt charts are easier to change as a task moves along and it comes closer to completion.

Accuracy

Gantt charts are simpler to read, but PERT charts extend an element of detail to the project scheduling through both the network model's ability to display dependency and PERT's unique ability to anticipate actual time that a task will take to completion. Tasks in PERT charts will have three representative time structures: optimistic, most likely, and pessimistic. By averaging these times, a manager can predict how long a task will actually take to complete more realistically than the single time that Gantt charts provide.

They are methods using for managing a projects as well as controlling & plans updating and  progressing of phases related with the project life 

PERT – Program Evaluation and Review Technique Developed by Lockheed Corporation in participation with the US Navy Polaris Missile/Submarine Project in1958

CPM – Critical Path Methoddeveloped by DuPont c.1958

Gantt Charts: Henry Gantt who the Gantt chart is named, worked for the department of defense during the First World War. The chart is widely used as a project management tool. The Gantt chart allows you to see start and stop date for project task and subtask.