Explain why digital systems store and process all data as binary, and describe how bits, nibbles and bytes represent numbers, text and other data.

What this dot point is asking

WJEC asks you to explain why every piece of data inside a digital device, whether a number, a letter, an image or a sound, is ultimately stored as binary, and to describe the basic units that binary is grouped into. This is the foundation of the whole Data topic: images, sound and file sizes all build on the idea that data is a pattern of 0s and 1s. The exam tests both the reason behind binary and the unit vocabulary (bit, nibble, byte), so you need the concept and the precise terms.

Why everything is binary

A computer is built from huge numbers of tiny electronic switches. Each switch is either on or off, carrying a high or a low voltage. There is no convenient "third state", so the natural number system to use is one with exactly two symbols.

Because the electronics only ever has to distinguish two values, the system is robust: a voltage does not have to be an exact level, just clearly "high" or "low", so minor electrical noise does not flip the meaning of the data. This reliability is the real reason binary is used, and it is the answer examiners want, not simply "computers only understand 0 and 1".

Bits, nibbles and bytes

Binary digits are grouped into standard units.

A single bit can only be 0 or 1, so on its own it can represent just two things, such as yes or no. To represent more, bits are combined. The number of different patterns grows quickly: each extra bit doubles the possibilities.

How binary represents different data

The same binary patterns are reused to mean different things depending on context.

• Numbers are stored directly as binary place values: the byte 00001101 is $8 + 4 + 1 = 13$.
• Text is stored using a character set, where each character is given a binary code (for example, a standard code assigns a number to each letter, digit and symbol, which is then stored in binary).
• Images and sound are first turned into numbers (covered in their own dot points), and those numbers are stored in binary.

The crucial idea for the exam is that the binary on its own has no meaning: the same byte can be a number, a letter or part of a sound. It is the software that decides how to interpret each pattern.

Why this matters

Binary is the bedrock of every other Data idea in the specification. File sizes are measured in bytes and their multiples; image and sound files are large precisely because each pixel or sound sample is stored as several bytes of binary; and compression works by reducing the number of binary patterns that must be stored. Understanding that everything reduces to bits, and that $2^n$ controls how much a group of bits can represent, lets you reason about all of these confidently.