Six gate symbols, six jobs

4 minAS Level3.2.13.2.2

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can recognise NOT, AND, OR, NAND, NOR and XOR symbols, and say exactly when each outputs 1.

A gate is a tiny rule machine

Each input is either 0 (false/off) or 1 (true/on). The gate applies one simple rule and sends out one result.

For a two-input gate, call the inputs A and B. For example, with A=1 and B=0, AND gives 0 because both inputs are not 1; OR gives 1 because at least one input is 1.

The standard symbols are worth learning by sight. A small output circle, called an inversion bubble, means “flip the output”.

Definition

Logic gate functions

NOT outputs the opposite of its single input.
AND outputs 1 only when both inputs are 1.
OR outputs 1 when at least one input is 1.
NAND is NOT-AND: it outputs 0 only when both inputs are 1.
NOR is NOT-OR: it outputs 1 only when both inputs are 0.
XOR (also called EOR) outputs 1 when the two inputs differ — exactly one is 1.

Every gate except NOT has two inputs. A bubble at the output flips the usual result: AND becomes NAND; OR becomes NOR.

Read the symbol

Multiple choiceQuestion 1 · Recall

An AND-shaped symbol has a small circle at its output. Which gate is it?

ANANDBNORCXORDNOT

One-line answerQuestion 2 · Recall

How many inputs does a NOT gate have?

Answer the 2 questions above to continue.

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