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A curved-back shield shape, outputting true when any input is true.
Also known as: OR gate, Shield shape logic, Curved back gate
The shield-shaped OR gate outputs true when any input is. Its curved back is the entire difference from the AND gate's flat one, which is a small visual difference for opposite logic.
Outputs a true signal when at least one of its inputs is true, implementing inclusive disjunction in hardware.
Contexts: Technical drawing, Electrical equipment
Differs from the AND gate only in having a curved rather than straight back, which is a small visual distinction carrying opposite logic.
Contexts: Technical drawing, Electrical equipment
Is drawn two different ways by two different standards. The international form defined by the IEC is a plain rectangle containing the label ≥1; the form defined by the American ANSI and IEEE standards is a curved shield shape with a concave back and a pointed front. Neither is a mistake and neither is old-fashioned — a reader meeting an unfamiliar drawing of a familiar component is usually looking at the other continent's standard rather than at an error.
Contexts: Technical drawing, Electrical equipment
Related forms that are not treated as separate canonical symbols — see our variant rules.
IEC rectangular form
A rectangle labelled ≥1 — read as 'one or more inputs are true', which is exactly what an OR gate does.
ANSI distinctive-shape form
The pointed shield outline. Adding a second curve across its back makes it exclusive-OR, which is a distinction the rectangular form makes by changing the label to =1.
A shape with a concave curved back and two convex curves meeting at a point on the right, with input lines entering the back and one output leaving the point.
Curved back against flat back, for opposite logic.
The basic logic gate symbol set.
The same operation in hardware and in formal logic.