A CNC (Computer Numerical Control) controller is a device used to manage the operation of a CNC machine, which is a type of automated manufacturing equipment used in industries such as aerospace, automotive, and machining. 

The CNC controller receives instructions from a computer-aided design (CAD) program that specifies the sequence of operations required to complete a specific task. The controller then translates these instructions into electrical signals that drive the CNC machine's motors and other mechanical components, such as spindles, cutting tools, and probes.

CNC controllers typically have several different components that work together to execute tasks. The main components include a computer, a motor control board, and I/O (input and output) modules. The computer has software installed that provides a graphical user interface (GUI) that the operator uses to input instructions into the controller.

The motor control board receives instructions from the computer and translates them into signals that are sent to the machine's motors. The I/O modules are used to control the operation of other machine components, such as pumps, solenoids, and lights.

In summary, a CNC controller is an essential component of a CNC machine, responsible for interpreting the instructions provided by a CAD program, and translating them into the electrical signals necessary to move the machine's motors and other components to complete a manufacturing task.