Rice cookers and steamer may be divided into rice cooking sauce pans or pots (risotto pan, paella pan, porridge pot), rice steamers (e.g., 蒸籠 (zhēng lóng)), ceramic or plastic containers for microwave ovens, and gas and electrical appliances. Most dedicated home rice cookers are of the electric type. In commercial or industrial use, there are many varieties, such as large gas or electric rice cookers, a large-scale rice cooker that is called a "rice boiler", and fully automatic versions which handle the whole process of rice cooking from washing rice to the end of the cooking cycle. Dedicated rice cookers date from long ago in human history. A ceramic rice steamer dated to 1250 BC is on display in the British Museum.
Cooking rice has traditionally required constant attention to ensure the rice was cooked properly. Electric rice cookers automate the process by mechanically or electronically controlling heat and timing, thus freeing up a heating element on the cooking range that had to be otherwise occupied for rice cooking. Although the rice cooker does not necessarily speed up the cooking process, with an electric rice cooker the cook's involvement in cooking rice is reduced to simply measuring the rice, preparing the rice properly and using the correct amount of water. Once the rice cooker is set to cook, the rice will be cooked with no further attention. Many modern cookers have a heat-insulating casing and a warming mechanism. When the rice is determined to be fully cooked, the unit will automatically switch to the "keep warm" cycle, thus preventing the rice from being overcooked and keeping the rice warm until it is ready to be served. The degree of insulation provided by the casing can also be used to keep cold solids cold.