13. Data Representation
User-defined data types, file organisation and access, floating-point representation, normalisation and rounding errors.
Statometer75BankerNext Paper 395%Everything for this topic — study hub
A2 Level · 9618 · Paper 3
Statometer — what 32 real papers say about this topic and each of its 3 syllabus bullets
Banker · #3 of 8 in A2 Level · recomputed with every new session
Set in nearly every paper and worth a big slice of it — revise first, expect it.
- Next Paper 3
- 95%
- 9 in 10 chance it is set
- Marks a paper
- 16.4 / 75
- 22% of Paper 3 · fair share 17%
- Appeared in
- 32 / 32
- Paper 3 sittings 2021–2026
- Last set
- May/Jun 2026
- 9618/33 · Q5 · 7 marks · 11-series streak
What the papers say
- Set in 32 of 32 Paper 3 sittings on the current syllabus — treat it as certain.
- Worth about 16.4 marks a paper (22% of Paper 3, 1.3× its fair share).
- Last set May/Jun 2026 · 9618/33 · Q5 for 7 marks — in the most recent series.
- Set in each of the last 11 series without a miss.
- Steady at around 15.9 marks a paper year on year.
- Lives on “Write” and “Show” — 61% of its questions: you must produce something — code, a diagram, a table — practise doing it, not reading it.
- Its biggest question so far: 14 marks (May/Jun 2021 · 9618/31 · Q1).
- Inside the topic, §13.1 User-defined data types carries the most marks (45%) and §13.2 File organisation and access the least (13%).
- It is examined mostly as AO2 (Apply & analyse, 61%), the rest AO1 (39%) — you must apply it to the given data or scenario — work it out, trace it, explain it in context.
- The examiner has commented on 44 of its questions — read “What the examiner said” before you practise.
- The single biggest share of Paper 3 among its 6 topics.
Command words
Share of questions using the word (a question can use several). What each wants →
Question shapes
- ≤ 6 mk57
- 7–9 mk23
- 10–12 mk1
- 13–15 mk3
- 16+ mk0
Average 6.3 marks a question · 5% with a figure or table · 39% with code · biggest 14 marks
Assessment objectives — how it is examined
Every part of every current-syllabus question filed under Cambridge's AO1 / AO2 / AO3 (from its command word and what it asks you to do), so you know whether this topic pays for definitions, for applying, or for judging and building.
- AO1 Knowledge & understanding
- AO2 Apply & analyse
- AO3 Design, program & evaluate
Paper 3 as a whole
| Paper 3 | Syllabus | Measured |
|---|---|---|
| AO1 Knowledge & understanding | 60% | 54% |
| AO2 Apply & analyse | 40% | 46% |
| AO3 Design, program & evaluate | 0% | 0% |
Syllabus = Cambridge's grid; measured = the bank's current-syllabus papers.
Inside the topic — every syllabus bullet, measured
Each part of each question is filed under the bullet it examines; the numbers are per Paper 3 sitting, exactly like the topic's. Open a bullet for its own Statometer.
13.1User-defined data types#3 of 14 on Paper 3Banker · 8895% next paper6.7 marks32/32 sittings→ May/Jun 2026Banker · 8895%
6.7 · 45% of topic32/32May/Jun 2026latest series · →Asked in nearly every paper — the bullet to know cold.Syllabus: why they are needed; non-composite types (enumerated, pointer); composite types (set, record, class/object); designing a type for a problem
- Next Paper 3
- 95%
- 9 in 10
- Marks a paper
- 6.7
- 9% of the paper · 45% of the topic
- Asked in
- 32 / 32
- Paper 3 sittings · 43 questions
- Last asked
- May/Jun 2026
- 9618/33 · Q1 · 5 marks · 11-series streak
- Asked in 32 of 32 Paper 3 sittings — nearly every paper.
- About 6.7 marks a paper (9% of Paper 3; 45% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 9618/33 · Q1 (5 marks) — in the most recent series.
- Asked in each of the last 11 series.
- Usually “Write” or “Describe”: you must produce something — code, a diagram, a table — practise doing it, not reading it.
- Biggest chunk of marks so far: 10 in Oct/Nov 2022 · 9618/32 · Q4.
- It is examined mostly as AO2 (Apply & analyse, 61%), the rest AO1 (39%) — you must apply it to the given data or scenario — work it out, trace it, explain it in context.
Last 12 sittings→ SteadyAssessment objectives
AO1 39%AO2 61%- AO1 Knowledge & understanding
- AO2 Apply & analyse
- AO3 Design, program & evaluate
- Write54%
- Describe35%
- State23%
- Explain19%
13.2File organisation and access#12 of 14 on Paper 3Regular · 3549% next paper2.1 marks14/32 sittings↗ May/Jun 2026Regular · 3549%
2.1 · 13% of topic14/32May/Jun 2026latest series · ↗Set most sessions for a few marks; know the definition and one example.Syllabus: serial, sequential (key field) and random (record key) organisation; sequential vs direct access; hashing algorithms for reading and writing records
- Next Paper 3
- 49%
- 2 in 4
- Marks a paper
- 2.1
- 3% of the paper · 13% of the topic
- Asked in
- 14 / 32
- Paper 3 sittings · 15 questions
- Last asked
- May/Jun 2026
- 9618/32 · Q4 · 3.5 marks
- Asked in 14 of 32 Paper 3 sittings — roughly one paper in 2.
- About 2.1 marks a paper (3% of Paper 3; 13% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 9618/32 · Q4 (3.5 marks) — in the most recent series.
- Rising: 1.7 → 2.3 marks a paper.
- Usually “Describe” or “Outline”: full sentences with a reason, not one-word answers.
- Biggest chunk of marks so far: 6 in May/Jun 2024 · 9618/32 · Q7.
- It is examined mostly as AO1 (Knowledge & understanding, 67%), the rest AO2 (33%) — definitions and descriptions in syllabus words score.
Last 12 sittings↗ RisingAssessment objectives
AO1 67%AO2 33%- AO1 Knowledge & understanding
- AO2 Apply & analyse
- AO3 Design, program & evaluate
- Describe47%
- Outline40%
- State40%
- Complete40%
13.3Floating-point numbers#4 of 14 on Paper 3Banker · 8190% next paper6 marks29/32 sittings↘ May/Jun 2026Banker · 8190%
6 · 42% of topic29/32May/Jun 2026latest series · ↘Asked in nearly every paper — the bullet to know cold.Syllabus: mantissa and exponent in two's complement; converting to and from denary; normalisation; precision, underflow, overflow and rounding errors
- Next Paper 3
- 90%
- 9 in 10
- Marks a paper
- 6
- 8% of the paper · 42% of the topic
- Asked in
- 29 / 32
- Paper 3 sittings · 29 questions
- Last asked
- May/Jun 2026
- 9618/33 · Q5 · 7 marks · 8-series streak
- Asked in 29 of 32 Paper 3 sittings — nearly every paper.
- About 6 marks a paper (8% of Paper 3; 42% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 9618/33 · Q5 (7 marks) — in the most recent series.
- Asked in each of the last 8 series.
- Easing: 6.9 → 5.9 marks a paper.
- Usually “Show” or “Calculate”.
- Biggest chunk of marks so far: 14 in May/Jun 2021 · 9618/31 · Q1.
- It is examined almost entirely as AO2 (Apply & analyse, 76%) — you must apply it to the given data or scenario — work it out, trace it, explain it in context.
Last 12 sittings↘ EasingAssessment objectives
AO1 24%AO2 76%- AO1 Knowledge & understanding
- AO2 Apply & analyse
- AO3 Design, program & evaluate
- Show90%
- Calculate69%
- Explain38%
- Write38%
10% of the topic's marks sit in question parts that belong to another topic (scenario questions cross sections) or that no bullet claims; they count for the topic, not for a bullet.
Marks a paper, year by year
By exam series
- May/Jun18/18 · 15.9 mk
- Oct/Nov14/14 · 17.4 mk
What you need to know3syllabus §13.1, §13.2, §13.3
- 13.1User-defined data types — why they are needed; non-composite types (enumerated, pointer); composite types (set, record, class/object); designing a type for a problem
- 13.2File organisation and access — serial, sequential (key field) and random (record key) organisation; sequential vs direct access; hashing algorithms for reading and writing records
- 13.3Floating-point numbers — mantissa and exponent in two's complement; converting to and from denary; normalisation; precision, underflow, overflow and rounding errors
Video lectures23ZAK's YouTube channel · play here
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Infographics2draw these the way the examiner expects · download as PNG
Floating-point representation
File organisation & hashing
Key terms13use these exact words in the exam
Dotted terms are defined in the glossary.
Code help3referenced to the Cambridge pseudocode guide
TYPE Season = (Spring, Summer, Autumn, Winter)TYPE TIntPointer = ^INTEGERDECLARE ThisSeason, NextSeason : SeasonDECLARE MyPointer : TIntPointerDECLARE Count : INTEGERThisSeason ← SpringNextSeason ← ThisSeason + 1Count ← 41MyPointer ← ^CountMyPointer^ ← MyPointer^ + 1OUTPUT NextSeason, " ", Count
// 8-bit mantissa 0.1100000 (two's complement, = 0.75) and exponent 0011 (= 3)DECLARE M : REALDECLARE E : INTEGERM ← 0.75E ← 3OUTPUT M * 2 ^ E // 6.0
FUNCTION Hash(Key : INTEGER) RETURNS INTEGERRETURN Key MOD 7 + 1 // 7 buckets, addresses 1..7ENDFUNCTIONOUTPUT Hash(1234), " ", Hash(1241), " ", Hash(500) // 1241 collides with 1234
Playground examples6runnable programs for this topic
- Run
Random-access file — SEEK, PUTRECORD, GETRECORD
Records are stored at addresses; SEEK moves the file pointer, then read or write the record there.
A2PseudocodeFile handling §9.2 - Run
Hashing to a record address
A hash function turns a key into a file address so a record is found directly, without searching.
A2PseudocodeFile handling 9618 §13.2, §9.2 - Run
Enumerated, pointer & set types (§4)
The three non-record user-defined types from the guide, in one program.
A2PseudocodeRecords & user-defined types §4.1–4.2 - Run
Records with DATE fields & whole-record copy
The guide's StudentRecord: Pupil2 ← Pupil1 copies every field; arrays of records are updated in a loop.
A2PseudocodeRecords & user-defined types §4.1–4.2 - Run
Floating-point → denary
An 8-bit two's complement mantissa and a 4-bit two's complement exponent, converted to a denary value.
A2PseudocodeTheory in code 9618 §13.3 - Run
Binary, hex and two's complement
bin(), hex(), int(s, 2) and format() — plus two's complement of a negative number by hand.
O LevelASPythonTheory in code 2210 §1 / 9618 §1
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