Dairy farming is a class of agriculture for the long-term production of milk, which is processed for the eventual sale of a dairy product. Dairy farming has a history that goes back to the early Neolithic era, around the seventh millennium BC, in many regions of Europe and Africa. Before the 20th century, milking was done by hand on small farms. Beginning in the early 20th century, milking was done in large scale dairy farms with innovations including rotary parlors, the milking pipeline, and automatic milking systems that were commercially developed in the early 1990s.