Printers that can print on both sides of a piece of paper are called duplex printers. They work by either reversing the sheet of paper back into the printer after a single page is done or by simultaneously printing on both sides.
Printers that lack automatic duplex printing can still be used to manually perform duplex printing. After a single side of the paper has been printed, the operator manually inserts the printed page back into the printer so that the unprinted side is printed on. Most operating systems support both manual and automatic duplex printing.Learn more about Printers