A kitchen stove, usually called a stove (especially but not only in US English), range, cooker, or oven is a kitchen appliance designed for the purpose of cooking food. Kitchen stoves rely on the application of direct heat for the cooking process and may also contain an oven, used for baking. In the industrialized world, as stoves replaced open fires and braziers as a source of more efficient and reliable heating, models were developed that could also be used for cooking, and these came to be known as kitchen stoves. When homes began to be heated with central heating systems, there was less need for an appliance that served as both heat source and cooker and stand-alone cookers replaced them. Cooker and stove are often used interchangeably. The fuel-burning stove is the most basic design of kitchen stove. Nearly half of the people in the world (mainly in the developing world), burn biomass (wood, charcoal, crop residues, and dung) and coal in rudimentary cookstoves or open fires to cook their food. [ ] More fuel efficient and environmentally sound biomass cook stoves are being developed for use there. Modern kitchen stoves may use alternative methods for heating food. Natural gas and electric stoves are the most common today in western countries. Both are equally effective and safe, and the choice between the two is largely a matter of personal preference and pre-existing utility outlets: if a house has no gas supply, adding one just to be able to run a gas stove is an expensive endeavor. In particular, professional chefs often prefer gas cooktops, for they allow them to control the heat more finely and more quickly. On the other hand, some chefs often prefer electric ovens because they tend to heat food more evenly. Today’s major brands offer both gas and electric stoves, and many also offer dual-fuel stoves combining gas cooktops and electric ovens. Modern kitchen stoves have both burners on the top (also known as the cooktop or stovetop in American English and as the hob in British English) as well as an oven. A cooktop can refer to the top of a stove or burners built into a countertop. Many newer cooktops are made of glass-ceramic. A drop-in range has both burners on the top and an oven and hangs from a cutout in the countertop (that is, it cannot be installed free-standing on its own). Most modern stoves come in a unit with built-in extractor hoods.