The 4000 series is a family of integrated circuits which implement a variety of logic functions using CMOS (Complementary Metal–Oxide–Semiconductor) technology, and are still in use today.
4000 series parts have the advantage of lower power consumption, wider range of supply voltages (3V to 15V), and simpler circuit design due to the vastly increased fanout.
However their slower speed (initially about 1MHz operation, compared with bipolar TTL's 10MHz) limits their applications to static or slow speed designs.