What is it
Binary is a number system that uses only two digits, 0 and 1, instead of the usual ten (0–9). Every piece of data a computer stores or processes — numbers, letters, images, sound — is ultimately represented as binary.
Why it matters
Computers are built from electronic switches that are only ever fully on or fully off — exactly what a 0 or 1 represents. Understanding binary is understanding the actual language computers think in, underneath every app and website.
Exam tip
Practice converting small numbers (up to 255) between denary and binary until it's automatic — this comes up constantly, and the place-value method (128-64-32-16-8-4-2-1) is always testable.
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