Using only a few transistors, the first integrated circuits—known as “small-scale integration” (SSI)—were critical to early space projects. The Minuteman missile and Apollo projects purchased nearly all integrated circuits available between 1960 and 1963. By the end of the 1960s, integrated circuits began to appear in consumer products. After SSI, also at the end of the decade, began work toward developing circuits with hundreds of transistors on each chip. By the mid 1970s, chips with tens of thousands of transistors were available and used for computer memories and second-generation microprocessors.