The big idea: Everything a computer stores is bits. A photo, a song and a spreadsheet are all just long runs of 1s and 0s.
What makes them different: The agreement about how to read them — and that agreement lives in the program, never in the bits.
One byte, 01000001, read four different ways. The bits never change.
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A character set is a lookup list: Everyone agrees in advance that 65 means A, 66 means B, and so on.
Store the number, and any program that knows the same list can show the right letter.
Integers
- Stored by place value — the columns double
- One byte holds 0 to 255
- Bigger numbers simply use more bytes
- One extra bit can mark the number as negative
Characters
- A character set assigns each character a number
- ASCII — one byte per character, enough for English
- Unicode — every writing system, using more bytes when needed
- The character itself is never stored; only its number
Strings
- A string is characters stored one after another
- "CAT" is 67, 65, 84 — three bytes in a row
- The computer also needs to know where the string ends
- That is why a long name takes more storage than a short one
Why the same byte can be two things: 01000001 is 65 if a program is reading numbers and A if it is reading text.
Opening a file with the wrong program shows nonsense for exactly this reason: the bits are fine, the agreement is wrong.
Software that works in every language: Unicode stores every script. Programming languages add locale settings (dates, currency and decimal marks shown the local way), resource files that keep interface text outside the code so it can be translated, and right-to-left layout for Arabic and Hebrew.
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Measure it, then store the measurements: Pictures and sound are not naturally made of numbers. So the computer samples them — takes many small measurements — and stores those.
More measurements means more detail, and more storage.
Images — one measurement per pixel
The picture is divided into a grid of pixels. Each pixel's colour is stored as numbers: one byte for a shade of grey, or three bytes for red, green and blue.
A 1000 × 1000 colour photo is three million bytes before any compression.
Audio — thousands of measurements a second
The height of the sound wave is measured many thousands of times per second, and each measurement is stored as a number.
Measuring more often, or storing each measurement more precisely, gives better sound and a bigger file.
Video — images plus audio, many times a second
Video is a sequence of complete images, typically 24 to 60 every second, with the audio stored alongside.
That is why video files are by far the largest — and why they are always compressed.
What this costs you: Storage and retrieval both scale with the number of measurements.
A bigger file needs more room, takes longer to read from storage, and takes longer to send over a network — which is the reason compression exists.
How this is tested — you must explain the ENCODING — what is measured, and what number gets stored. It comes up two ways:
Paper 1 Section A
- Explain how a stated data type is stored, 2-4 marks
- Say why one file is larger than another
- Link detail or quality to storage size
Paper 1 Section B — case study
- Explain the storage needs of the case study's data
- Justify a format or a quality setting from them
The classic trap: Answering "it is stored as 1s and 0s". Everything is. The mark is for saying what was measured and what number was stored — brightness per pixel, wave height per sample.
Explain how a colour photograph is stored in binary, and why increasing its resolution increases the file size.
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