How Should It Be Stored? Data Representation Drill
Computer Systems revisionApprox 25–35 min6 scenarios · justification practice
Recap: Whole numbers are stored as binary integers; numbers with a fractional part use floating point (mantissa and exponent). Text uses extended ASCII (8 bits, 256 characters) or Unicode (16 bits, 65,536+ characters for every language). Images are bitmaps (a grid of pixels) or vectors (objects with attributes).
→ Full lesson: CS2 — Text
How to use this drill: Each scenario needs a way of storing data. Choose the best representation, then justify it with a detail from the scenario. Each scenario has its own two choices. Reveal the model answer to check your reasoning.
Your choices and justifications are saved automatically.
Section C — Data Representation
6 scenarios. Choose an answer, justify it using the scenario, then check the model answer.
Scenario 1 of 6Lives left in a game
A game stores how many lives the player has left. The value is always a whole number from 0 to 9.
Expected: Binary integer
A binary integer. The number of lives is always a whole number with no fractional part, so it can be stored exactly as a positive binary integer. Floating point is only needed for real numbers such as 6.5.
Scenario 2 of 6Weather station
A school weather station records the outdoor temperature every hour, for example 14.75 °C and 9.5 °C.
Expected: Floating pointFloating point. The readings are real numbers with a fractional part, such as 14.75. Floating point stores them as a mantissa (the significant digits) and an exponent (how far to move the binary point).
Scenario 3 of 6Worldwide chat app
A messaging app will be used in many countries. Users write in English, Chinese, Arabic and Hindi, and often use emoji.
Expected: UnicodeUnicode. Extended ASCII can represent only 256 characters, mostly English letters, digits and symbols. Unicode uses 16 bits, so it can represent 65,536+ characters, enough for the characters of all the world's languages, plus emoji.
Scenario 4 of 6Very small memory
A pocket calculator displays short English messages such as "ERROR" and "LOW BATTERY". It has a very small amount of memory.
Expected: Extended ASCIIExtended ASCII. Only English letters are needed, which ASCII covers, and each character uses 8 bits instead of Unicode's 16. That halves the memory needed for the messages, which matters when memory is very limited.
Scenario 5 of 6School logo
The school logo is made of simple shapes and must be printed on a small badge and also on a large banner without losing quality.
Expected: Vector
A vector graphic. It is stored as objects (e.g. rectangle, ellipse, polygon) with attributes such as coordinates, fill colour and line colour. It is redrawn from these at any size, so it does not become pixelated when enlarged for the banner.
Scenario 6 of 6Sports day photograph
A photographer takes a picture of the school sports day to put on the school website.
Expected: Bitmap
A bitmap. A photograph has continuous detail and colour changes from pixel to pixel, which cannot be described as a small number of shapes. A bitmap stores the colour of every pixel, so it can show this detail.
Marker's eye view — why candidates lose marks
When comparing bitmap and vector, examiners want a reason linked to the scenario: "the logo must be resized, and a vector graphic is redrawn from its attributes so it does not pixelate". Writing "vectors are better quality" gets nothing.
For text, quote the numbers: extended ASCII uses 8 bits for 256 characters; Unicode uses 16 bits for 65,536+ characters. Then link the choice to the languages or memory in the scenario.