A transistor computer, now often called a second generation computer, is a computer which uses individual transistors instead of vacuum tubes. The first generation of electronic computers used vacuum tubes, which were big, unreliable, and generated large amounts of heat. A second generation of computers, through the late 1950s and 1960s contained circuit boards filled with individual transistors and magnetic core memory. These machines were in use up to the late 1960s, when integrated circuits became available.