4000-series integrated circuits

The 4000 series is a CMOS logic family of integrated circuits (ICs) first introduced in 1968 by RCA. It had a supply voltage range of 5V to 20V, which is much higher than any contemporary logic family.
Almost all IC manufacturers active during this initial era fabricated models for this series. It's naming convention is still in use today.
History.
The 4000 series was introduced as the "CD4000 COS/MOS" series in 1968 by RCA as a lower power and more versatile alternative to the 7400 series of transistor-transistor logic (TTL) chips. The logic functions were implemented with the newly introduced Complementary Metal–Oxide–Semiconductor (CMOS) technology. While initially marketed with "COS/MOS" labeling by RCA (which stood for Complementary Symmetry Metal-Oxide Semiconductor), the shorter "CMOS" terminology emerged as the industry preference to refer to the technology. The first chips in the series were designed by a group led by Albert Medwin.
Wide adoption was initially hindered by the comparatively lower speeds of the designs compared to TTL based designs. Speed limitations were eventually overcome with newer fabrication methods, leaving the older TTL chips to be phased out. The series was extended in the late 1970s and 1980s with new models that were given 45xx and 45xxx designations, but are usually still regarded by engineers as part of the 4000 series. In the 1990s, some manufacturers (e.g. Texas Instruments) ported the 4000 series to newer HCMOS based designs to provide greater speeds.
Design considerations.
The 4000 series facilitates simpler circuit design through relatively low power consumption, a wide range of supply voltages, and vastly increased load-driving capability (fanout). This makes the series ideal for use in prototyping LSI designs. While TTL based design is similarly modular, it requires meticulous planning of a circuit's electrical load characteristics. Buffered models can accommodate higher electrical currents, but have a greater risk of introducing unwanted feedback. Many models contain a high level of integration, including fully integrated 7-segment display counters, walking ring counters, and full adders.