Typically, two separate cartridges are inserted into a printer: one containing black ink and one with each of the three primary colors. Alternatively, each primary color may have a dedicated cartridge. Some cartridges are specifically designed for printing photographs. All printer suppliers produce their own type of ink cartridges. Cartridges for different printers may be incompatible - either physically or software-wise. Since replacement cartridges from the original manufacturer of the printer are often very expensive, some other manufacturers produce "compatible" cartridges as cheaper alternatives. Some cartridge have incorporated the printer's head (most HP printers use this system). Usually, they are more expensive, but the printers are cheaper. Others don't include the printer head, but they are more economic and the printers are more expensive (for example, most Epson printers)