The transit of paper through the printer begins at the paper feed. Two types of paper feed are common. In a "tractor" feed, the paper has an additional centimeter of paper on each edge with holes along the margin. As toothed wheels inside the printer rotate, the teeth fit into the holes and draw the paper in. This keeps the paper in proper alignment as it is fed through the printer. The pages are joined as one long, continuous page with perforations on the page breaks and holed margins. The output area usually has a sharp plastic edge on some part of it so that the paper may be torn against it as even finely perforated paper can tear inappropriately. This type of paper and paper feed are most common in dot-matrix and daisy wheel printers. In "friction" feed printers, a roller is used which catches and rolls the page forward, similar to a typewriter. This allows you to use either the continuous feed paper mentioned above, or single sheet paper like typing paper, which doesn't have the tractors. The disadvantage is that the paper occasionally does not stay aligned as it goes through the printer. To guide the paper into the printer, there are usually marks on either side of the feed. This type is preferred by many people because the paper does not need to be torn to separate it, and one need not buy specially-holed printer paper. Any normal typing or copier paper will do, even stationery.