Printing

Duplex printing is a feature of computer printers and multifunction printers (MFPs) that allows the automatic printing of a sheet of paper on both sides. Print devices without this capability can only print on a single side of paper, sometimes called simplex printing.

Consumer and low-to-medium volume office printers use a duplexing unit that reverses a piece of paper after the first side has been printed. Often, on MFPs, this is combined with a reversing automatic document feeder (RADF) to allow for duplex scanning also. Higher volume printers may in essence have two print engines in a single device, and are able to print both sides of the paper in a single pass.

Duplex print devices, depending on options, software, and printer settings, can print single-sided page to single-sided page (1:1) or double-sided page to double-sided page (2:2). Many can also combine single-sided pages into a double-sided page format (1:2). Double-sided booklet formats (2:2 with a center fold) are also available, depending on optional outputs from the printer.

Duplexed documents can be printed as if to be bound on either the short edge or the long edge. Long edge binding in portrait mode allows for pages to be turned side-to-side like a book, and the pages be right side up. Short edge binding allows the pages to be oriented correctly if they are flipped vertically, as in a notepad. This second form of printing/binding is sometimes known as "tumble." If the printing is done in landscape mode, these concepts are transposed since the print direction is different.

Simplex printers can still print duplex jobs; however, the user has to manually turn the print job over and re-initialize the printing of the document.

In commercial printing (books, magazines, newspapers, etc.), the term applied to imparting an image to both sides of the substrate at the same time is 'perfecting' and is commonly achieved—especially in lithography—by passing the substrate through a perfecting drum, thus turning the sheet over after the first side is printed. The turned sheet then continues its way through the press, being gripped at the opposite edge whilst the second side is printed. This in effect tumbles the job, therefore accurate sheet sizing is a must to ensure accurate backing up of the job.