Texas Instruments 4-circuit 2-input OR gate CMOS DIP14

74HCxx series C-MOS standard logic ICs.
Standard logic ICs were originally used to create any logic circuit in the days when LSIs had low integration density and PLDs did not exist.
NOT, AND, OR, FF, etc., are the smallest units of logic circuits, and are contained in a single circuit, and multiple required ones are used in combination. For this reason, the electrical characteristics of the inputs and outputs are standardized so that standard logic ICs of the same series can be directly connected.
Broadly divided into TTL and C-MOS, the input/output voltage and current specifications are different, so the connections require some ingenuity. (Usually, LSIs are designed to match one of these specifications.) In addition, the speed and operating voltage differ depending on the series.
The 74HCxx series is a representative C-MOS product. Unlike TTL products such as 74LSxx, it has a wide operating voltage range, so it can be used with either +5V or +3.3V systems.