A drum unit is a crucial component in laser printers and photocopiers. It contains a cylindrical drum that holds the toner and transfers the image onto paper. The drum is coated with a photosensitive material that reacts to light, allowing it to pick up toner in specific areas to create text and images. When the printer operates, a laser beam creates an electrostatic image on the drum's surface. The toner, which is a fine powder, adheres to the charged areas of the drum. Finally, the drum rolls over the paper, transferring the toner to produce the final printed document.