Boolean logic and gates

Boolean logic works with statements that can only be true or false. These values are written as True and False, or in circuits as 1 and 0. There is no third option, such as 0.5 or 'maybe'. A school locker is either locked or unlocked.

Computers use Boolean logic because their circuits have exactly two states: on and off. A switch inside a chip either lets current through, which we label 1, or blocks it, which we label 0. Every input and output in a logic circuit is therefore a single binary value.

A logic gate is an electronic component in a digital circuit. It receives one or two binary input values, applies a fixed rule, and returns a single binary output value. The rule is fixed: the same input values always give the same output. Inputs are labelled with letters such as A and B, and the output with a letter such as P.

The three gates you need

Gate	Inputs	Shape of the symbol
AND	2	Straight vertical back edge and a semicircular curved front. Two input lines enter the flat back; one output line leaves the curved front.
OR	2	The rear edge curves inwards, and the two long sides bow outwards to a sharp point on the output side. Two input lines enter the curved rear; one output line leaves the point.
NOT	1	A triangle aimed towards the output, with a tiny circle on the pointed end. The input line joins the flat rear edge; the output line comes from the circle.

Use the shape to tell them apart: AND has a flat back and rounded front, OR a curved back and pointed front, and NOT a triangle with a circle at its point. Only these three gates are needed; NAND, NOR and XOR are not in the specification.

Other accepted notation

You may write T and F instead of 1 and 0, or use gate symbols, or the letter V for OR, instead of a gate's name. Keep to one style throughout a table or answer.

The three gates you need

Other accepted notation

Practise this