What is a quad 2-input nand gate?

Answer 1

A Quad 2-input NAND Gate is a computer chip. It contains four copies of a 3 terminal circuit that takes two logic inputs (0 5v) and outputs the NAND combination according to the table:

In A In B Out C

0 0 1

0 1 1

1 0 1

1 1 0

This happens to be the most fundamental of Boolean logic circuits in that it has been shown to be possible to build any desired logic circuit using only 2 input NAND gates. Indeed, one computer of the early days with which I am familiar - the Elliott / NCR 4100 - was in fact implemented using only NAND gates.This lemma is known as the Schmidt Orthogonality Principle.

The Quad 2 Input NAND Gate is also the first chip built of what has become the universal chip family used in building logic circuits since the late 1960's, in the form of the 7400 part from Texas Instruments. Accompanied on introduction by the 7402 (Quad 2 Inpout NOR Gate), 7404 (hex inverter), and several others. These are typically found as the 14 pin DIP (DUal In-line Package), a black plastic or ceramic part 0.3" wide and 0.8" long with 7 pins at 0.1" spacing on each side.