There are two types of Drop On Demand (DOD) inkjet technology, valve-jet and high-resolution piezo. This family of technologies creates only the ink drops that are "demanded" to print the message.

Valve-jet
A series of valves drives individual nozzles for the printing of 7- or 16-dot alphanumeric characters in one or two lines of text. Valve-jet technology is primarily used for large character printing on boxes and other secondary packaging.

High-resolution Piezoelectric
Piezo printhead technology consists of a series of ink chambers with shared channel walls made of ceramic material. Voltage is applied to the piezo material, changing its shape which in turn forces the ink out through a micro-orifice. Piezo technology can produce up to 20,000 drops per second and gives very high print resolution.