CIE IGCSE | TOPIC 1 ASSESSMENT
DATA REPRESENTATION: END OF TOPIC REVIEW
Check your understanding of number systems, text, sound, images, storage and compression. Work independently before checking your answers.
BEFORE YOU BEGIN
Suggested time: 20–25 minutes. Complete sections A and B without notes. Write section C answers in your exercise book before revealing the marking guidance.
Sections A and B provide an automatic score out of 11, one point for each fully correct item. Section C has 10 suggested written marks, assessed separately. These are original practice questions, not an official Cambridge paper or grade boundary.
For calculations, show working in your book and enter the answer in the unit requested. Calculator use can follow your teacher’s instructions. Your answers remain only while this page is open.
C | EXAM-STYLE WRITING
Write in your exercise book before revealing the guidance. Section C assesses subject knowledge and gives you practice expressing it clearly. The first table reproduces the command-word meanings supplied from the Cambridge syllabus. The second gives practical writing guidance for this review.
| CIE command word | Meaning from the specification |
|---|---|
| Calculate | work out from given facts, figures or information |
| Compare | identify/comment on similarities and/or differences |
| Define | give precise meaning |
| Demonstrate | show how or give an example |
| Describe | state the points of a topic / give characteristics and main features |
| Evaluate | judge or calculate the quality, importance, amount, or value of something |
| Explain | set out purposes or reasons / make the relationships between things clear / say why and/or how and support with relevant evidence |
| Give | produce an answer from a given source or recall/memory |
| Identify | name/select/recognise |
| Outline | set out the main points |
| Show (that) | provide structured evidence that leads to a given result |
| State | express in clear terms |
| Suggest | apply knowledge and understanding to situations where there are a range of valid responses in order to make proposals / put forward considerations |
The command applies to the subject context. A brief identification does not need an essay; an explanation needs accurate links. Use the guidance below for the four commands in this written review.
| Command word | What your answer should do | Useful writing pattern |
|---|---|---|
| Describe | State the main features or relevant points; for a process, make the sequence clear. | First… Next… Finally… |
| Explain | Give reasons, purposes or clear relationships, supported by relevant subject knowledge. | …because…; therefore…; resulting in…; leading to… |
| Compare | Identify similarities and/or differences, addressing both things on the same basis. | Both…; whereas…; unlike… |
| Evaluate | Make a reasoned judgement about suitability or value in the given context. | A benefit is…; however…; therefore, for this purpose… |
BUILD A CLEAR EXPLANATION
Point → reason or mechanism → consequence. Connectives help show the relationship, but the technical link must be accurate. Adding “because” to an unsupported claim does not make it a good explanation.
Thin answer: “More pixels make the file bigger.”
Developed answer: “Increasing resolution increases the number of pixels. Because each pixel needs stored colour data, more bits are required when colour depth stays fixed, therefore the raw image size increases.”
Use because or because of to introduce a cause; therefore, resulting in or leading to to show a consequence. For comparison, use both and whereas. For evaluation, use however and finish with a justified judgement.
Write enough relevant detail for the marks available. Clear, concise sentences are better than padding. These are writing supports, not compulsory phrases or separate official language marks.
12 | REPRESENTING TEXT
[2 suggested marks]
Describe how the characters in a text message are represented for storage in a computer.
Sample answer: Each character is assigned a code from a character set. The codes are represented as binary values for storage.
- Characters are mapped to codes in a character set: one mark.
- The codes are represented in binary for storage: one mark.
Writing focus: state the relevant features precisely. “Computers use binary” alone leaves out the character-to-code mapping. Do not assume all character encodings use one byte per character.
13 | IMAGE SIZE
[3 suggested marks]
A school doubles both the width and height of an uncompressed image while keeping colour depth fixed. Explain why the raw image data becomes four times larger.
Sample answer: The pixel count is width multiplied by height. Doubling both dimensions therefore gives 2 × 2 = four times as many pixels. Because the bits stored per pixel remain unchanged, four times as many bits are needed for the raw image data.
- Pixel count is width × height: one mark.
- Doubling both dimensions produces four times the pixels: one mark.
- Fixed bits per pixel links that increase to four times the raw data: one mark.
Writing focus: explain the cause and its consequence. Include the fixed-depth condition; do not claim every compressed file would quadruple.
14 | COMPRESSION METHODS
[2 suggested marks]
Compare lossy and lossless compression in terms of what happens to the original information and whether it can be reconstructed exactly.
Sample answer: Lossless compression preserves the information needed for exact reconstruction, whereas lossy compression permanently discards some information. Therefore lossless decoding can recover the original data exactly, while lossy decoding cannot recover the discarded information from that compressed file alone.
- A linked comparison of preserved information versus discarded information: one mark.
- A linked comparison of exact recovery versus an approximation / inability to recover discarded information: one mark.
Writing focus: address both methods on each comparison point. “Lossless is better” is a judgement without a comparison. Do not claim lossless always produces a smaller file.
15 | CHOOSE FOR THE PURPOSE
[3 suggested marks]
A school keeps an editable audio master and publishes a short preview on a website. Evaluate the suitability of lossy compression for these two uses. Give a justified recommendation for each.
Sample answer: Lossy compression can reduce the preview’s file size, leading to lower storage and transfer requirements. However, it discards audio information, so quality may be reduced. For the website preview, it is suitable if the sound quality remains acceptable. For the editable master, I would keep a lossless or uncompressed copy because the original detail is needed for later editing and cannot be recovered from a lossy file alone.
- A relevant benefit of lossy compression linked to the preview: one mark.
- Information loss / quality limitation linked to the need for an editable master: one mark.
- Justified recommendations for both uses, reflecting those different requirements: one mark.
Writing focus: weigh the benefit against the limitation and make a contextual judgement. “Lossy is good” does not evaluate suitability. Alternative recommendations can earn credit if their assumptions and technical reasoning are sound.
CHECK YOUR WRITTEN COMMUNICATION
- Did I answer the command word, rather than just name facts?
- For explain, did I show an accurate reason or cause-and-effect link?
- For compare, did I address both things on the same point?
- For evaluate, did I weigh relevant factors and justify my judgement?
- Did I use precise terms and connectives naturally, without repeating or padding?
Self-assess using the suggested content marks, keeping the written total separate from your automatic score. Use the writing checklist to improve an answer rather than adding unofficial language marks.
YOUR NEXT REVISION STEP
Submit sections A and B to see suggested lessons to revisit.
For written work, revisit text representation, images and compression where needed.
This short review samples the topic; it does not assess every syllabus point. Also check hexadecimal conversions, two’s complement and run-length encoding using the full Topic 1 revision page.
Choose two weak areas, revisit their explanations and attempt a fresh example. A second attempt at the same questions shows learning from feedback, rather than an independent assessment.