Imaging drum
The light-sensitive cylinder in a laser printer where the page is drawn as electric charge before the toner sticks.
The imaging drum — usually an organic photoconductor (OPC) — is the heart of electrophotography. First the whole drum is charged evenly; then the laser sweeps across it and discharges the points that are to print black, forming an invisible charge image of the page. Toner powder is drawn to the discharged points, transferred to the paper and fused by the fuser unit, after which the drum is cleaned and recharged for the next revolution. In many printers the drum sits in the same cartridge as the toner and is replaced with it; in others it is a separate wear part. The principle is the one Chester Carlson invented for the photocopier in 1938.