IB DP Computer Science: Theme A -- Concepts of Computer Science

This guide covers Theme A – Concepts of Computer Science, for IB Diploma Programme Computer Science, first assessment 2027 (SL: 38 hours; HL: 72 hours, including the case study). For the full two-theme syllabus map, see the IB DP Computer Science syllabus guide.

Where this fits in the syllabus

Theme A asks “how does a computing system work?”, covered by four sub-topics studied identically by both SL and HL students (unlike Theme B, where B.4 is HL only). Theme B, by contrast, asks “how do we use a computing system to solve a problem?”, and is where programming, algorithm design and object-oriented programming live. Paper 1 draws its four topic-specific questions from Theme A, plus three further questions tied to a pre-released case study — so Theme A content routinely appears embedded in case-study scenarios, not just as standalone recall questions, meaning the case study cannot be revised separately from A.1–A.4.

Syllabus coverage

IB DP COMPUTER SCIENCE — THEME A: CONCEPTS OF COMPUTER SCIENCE

• A.1 Computer fundamentals — the hardware layer (CPU components: control unit, ALU, registers), the fetch-execute cycle, primary versus secondary storage; how all data types (number, text, image, sound) are ultimately represented as binary, measured in bits and bytes; the role of the operating system in managing hardware resources and mediating between applications and the machine
• A.2 Networks — network fundamentals (clients, servers, LAN versus WAN); the layered model of network communication and the role of protocols (e.g. TCP/IP, HTTP) in letting different systems exchange data reliably; data transmission concepts (packet switching, bandwidth, common causes of transmission error) and the internet’s decentralised architecture
• A.3 Databases — why structured data is organised into databases rather than flat files (reducing redundancy, preserving integrity, controlling access); the relational model (tables, records, fields, primary and foreign keys) and how relationships between tables are represented; querying data conceptually, independent of any one query language, to retrieve, filter and combine information across related tables
• A.4 Machine learning — the distinction between traditional rule-based programming and machine learning, where a system derives its own rules from data; core concepts including training data, features, and the difference between supervised and unsupervised learning; real-world applications and the ethical issues they raise (bias in training data, transparency of automated decisions, the environmental cost of training large models), treated as integral content rather than an optional add-on

How to approach it

Because Theme A is largely descriptive and conceptual rather than programming-based, the skill being tested is usually explanation of mechanism or evaluation of a design choice, not writing code — a strong A.1 answer on the fetch-execute cycle explains what each stage actually does to data in the registers, not just names the stages in sequence. Students sometimes over-invest revision time in Theme B because it feels more “practical,” but Paper 1 is worth an equal share of external assessment and draws entirely from Theme A plus the case study, so under-revising A.1–A.4 leaves real marks on the table independently of programming ability. Because the case study is pre-released, practise applying each of the four sub-topics directly to its specific scenario rather than revising Theme A only in the abstract, since three of Paper 1’s questions are built around that case study specifically.

Worked example: applying A.3 to an unfamiliar scenario

A case study describes a library that currently stores every loan record in a single spreadsheet, repeating the borrower’s full name and address on every row.

Problem identified:  storing borrower details repeatedly in every
                      loan row duplicates data (redundancy) and risks
                      inconsistency if a borrower's address is
                      updated in one row but not others

Relational fix:       split the data into two related tables --
                      Borrowers (with a primary key, e.g. BorrowerID)
                      and Loans (with a foreign key BorrowerID
                      referencing the Borrowers table)

Result:                borrower details are stored once, referenced
                       by key from each loan record, preserving
                       integrity and reducing redundancy -- the
                       relational model applied directly to the
                       case-study scenario, not just defined in the
                       abstract

This is the pattern Theme A exam questions typically reward: naming the specific concept (here, the relational model and the primary/foreign key relationship) and applying it to the specific detail given in the scenario, rather than defining the concept in isolation.

Common mistakes

Describing the fetch-execute cycle as a fixed sequence of named stages without explaining what each stage does to data in the registers. Confusing a primary key (uniquely identifies a record within its own table) with a foreign key (a field referencing a primary key in a different table) — these are tested as a pair, and mixing them up is one of the most common Theme A errors. Treating A.4 as purely technical and omitting the ethical dimension, when the course syllabus brief explicitly frames raising ethical issues as one of the course’s defining characteristics. Using everyday, informal LAN/WAN terminology rather than the syllabus’s own vocabulary (client, server, protocol) in exam answers.

Quick revision checklist

• Be able to explain, not just name, each stage of the fetch-execute cycle.
• Know the relational model well enough to redesign a flat-file scenario into related tables with primary and foreign keys.
• Learn at least two ethical issues machine learning applications can raise, alongside the technical concepts of A.4.
• Revise A.1–A.4 directly against the pre-released case study, not only in the abstract.
• Give Theme A revision time equal to Theme B, since Paper 1 draws entirely from Theme A plus the case study.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Sciences: Computer science, first assessment 2027, © 2024. Verified 2026-09-06.