What does controllers mean in computer science?

Answer 1

A controller is a device that controls another device. The simplest example is a game controller. It is used to control action in a game.

Then there are electronic controllers. They are IC chips that are used to provide control logic for electronic devices. A floppy drive would be connected to a controller chip that produces the control signals needed for the drive to operate.

Then there are microcontrollers which are essentially small computers on a single chip with limited functionality. They would be used in appliances, vehicles, implanted medical devices, etc. Some operate as slow as 4 KHz and only handle 4 bits of data.