NAND Gate

What is NAND Gate?

A two-input logic gate whose output is the inverse of AND: it is 0 only when both inputs are 1 and 1 in every other case; its symbol is the AND D shape with a small inversion circle on the output, and it is written X = A NAND B.

This definition is part of the Boolean Logic chapter in Cambridge O Level Computer Science.

Concepts related to NAND Gate

• AND Gate
• NOT Gate
• NOR Gate
• Truth Table

Examiner tips on NAND Gate

• Read the limits as instructions, not as background. “Circuits must be drawn for the statement given, without simplification” is not a hint about how examiners mark — it is the mark scheme. If the expression says NOT (A AND B), the circuit has an AND gate followed by a NOT gate. Replacing the pair with a single NAND gate changes the structure, and the structure is what is being assessed.
• When is a NAND gate the right answer, then? Whenever the thing you were given contains the word NAND, or whenever you are constructing an expression yourself from a statement that says “not both”. What you may never do is replace a given NOT (… AND …) with one. The gate is not forbidden; the substitution is.