NOR gate

By contrast, the OR operator is monotonic as it can only change LOW to HIGH but not vice versa.

A significant exception is some forms of the domino logic family.

The standard, 4000 series, CMOS IC is the 4001, which includes four independent, two-input, NOR gates.

The left diagram above show the construction of a 2-input NOR gate using NMOS logic circuitry.

This is due to the faster charge mobility in n-MOSFETs compared to p-MOSFETs, so that the parallel connection of two p-MOSFETs realised in the NAND gate is more favourable than their series connection in the NOR gate.

The original Apollo Guidance Computer used 4,100 integrated circuits (IC), each one containing only two 3-input NOR gates.