There are two main technologies used for ink-jet printers: continuous ink-jet technology and random ink-jet technology. The early ink-jet printers and the current large format ink-jet printers all use continuous ink-jet technology, while the current popular ink-jet printers generally use random ink-jet technology. Continuous ink-jet technology is represented by charge modulation. In random ink-jet system, ink is sprayed only when printing is required, so it is also called on-demand.