O Level Computer Science 2210 — both papers, free.
A complete study guide for Cambridge O Level Computer Science 2210, covering all 10 topics of the official syllabus for exams in 2026–2028.
How to use it: the two papers test completely different skills. Paper 1 is recall and explanation of computer systems; Paper 2 is doing — writing pseudocode, completing trace tables, drawing logic circuits. Reading alone will not prepare you for Paper 2; you have to write code by hand.
Note: no calculators are permitted in either paper, so all number conversions must be done by hand.
📄 10 plain-English chapter handouts →✎ Practice & self-test →
The papers
| Paper | Covers | Format | Time / marks | Weight |
|---|---|---|---|---|
| Paper 1 — Computer Systems | Topics 1–6 | Short-answer and structured questions; all compulsory | 1 h 45 min · 75 marks | 50% |
| Paper 2 — Algorithms, Programming and Logic | Topics 7–10 | Short-answer and structured questions plus a scenario-based question; all compulsory | 1 h 45 min · 75 marks | 50% |
No calculators are permitted in either paper. Binary, denary and hexadecimal conversions must be done by hand — which is why the conversion drills below matter.
Number conversion drills
| Denary | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hex | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
| Binary | 0000 | 0001 | 0010 | 0011 | 0100 | 0101 | 0110 | 0111 | 1000 | 1001 | 1010 | 1011 | 1100 | 1101 | 1110 | 1111 |
Overflow occurs when the result needs more bits than the register holds — with 8 bits, any result above 255 causes overflow and the answer stored is wrong.
Skill check: Convert 10110101 to denary and to hexadecimal.
Data representation
1.1Number systems
Computers use binary because their circuits have two stable states — on and off, represented as 1 and 0. Hexadecimal is used by people because it is much shorter than binary, easier to read and less error-prone, and converts cleanly (one hex digit = four bits).
Uses of hexadecimal: MAC addresses, IPv6 addresses, HTML colour codes, memory dumps, assembly language and error/debugging codes.
You must be able to convert between denary, binary and hexadecimal, add binary numbers, identify overflow, and perform logical binary shifts — all covered in the drills above. Also know two's complement for representing negative binary numbers: to negate, invert all the bits and add 1.
Represent −20 in 8-bit two's complement.
- +20 = 00010100
- Invert all bits: 11101011
- Add 1: 11101100
1.2Text, sound and images
| Data type | How it is represented | Key terms |
|---|---|---|
| Text | Each character has a unique binary code in a character set | ASCII (7/8-bit, limited to mostly English) and Unicode (many more bits, covers all world languages and emoji — but needs more storage) |
| Sound | The analogue wave is sampled at intervals and each sample stored as a binary value | Sample rate (samples per second) and sample resolution (bits per sample). Higher values → better quality but larger file |
| Images | Stored as a grid of pixels, each with a binary colour value | Resolution (number of pixels) and colour depth (bits per pixel). Higher values → better quality but larger file |
An image is 100 × 200 pixels with a colour depth of 8 bits. Calculate the file size in bytes.
- Total pixels = 100 × 200 = 20 000
- Total bits = 20 000 × 8 = 160 000 bits
- Bytes = 160 000 ÷ 8 = 20 000 bytes (about 19.5 KiB)
1.3Data storage and compression
| Unit | Equivalent |
|---|---|
| 1 nibble | 4 bits |
| 1 byte | 8 bits |
| 1 kibibyte (KiB) | 1024 bytes |
| 1 mebibyte (MiB) | 1024 KiB |
| 1 gibibyte (GiB) | 1024 MiB |
| 1 tebibyte (TiB) | 1024 GiB |
| Lossless compression | Lossy compression | |
|---|---|---|
| Data | No data is permanently removed; the original can be perfectly restored | Some data is permanently removed; the original cannot be restored |
| Method | Run-length encoding; storing repeated patterns once with an index | Reducing colour depth, sample rate or resolution; removing sounds outside human hearing |
| File size | Reduced less | Reduced much more |
| Use for | Text and program files, where every byte matters | Music, photos and video streaming, where slight quality loss is acceptable |
Why compress: faster transmission and downloads, less bandwidth used, less storage space needed, faster web page loading, smaller email attachments.
Data transmission
2.1Types and methods of data transmission
A data packet has three parts: a packet header (destination and sender addresses, packet number, and how many packets make up the whole message), the payload (the actual data) and a trailer (a way to identify the end of the packet, and an error-checking method).
Packet switching: data is split into packets that travel independently by whatever route is fastest, then are reassembled in order at the destination. Missing packets are re-requested.
| Transmission type | Description | Suits |
|---|---|---|
| Serial | One bit at a time down a single wire | Long distances — reliable, no skew, cheaper |
| Parallel | Several bits at once down multiple wires | Very short distances — faster, but bits can arrive skewed |
| Simplex | One direction only | Computer to printer |
| Half-duplex | Both directions, but one at a time | Walkie-talkie |
| Full-duplex | Both directions simultaneously | Phone call, broadband |
USB is a serial method: it is a universal standard, connectors only fit one way, it can supply power and is auto-detected — but cable length is limited and older versions have slower transfer rates.
2.2Methods of error detection
| Method | How it works |
|---|---|
| Parity check | A parity bit is set so the total number of 1s is even (even parity) or odd (odd parity). If the received byte's parity is wrong, an error occurred. Weakness: two errors in the same byte cancel out and go undetected. |
| Checksum | A value calculated from the data block is sent with it; the receiver recalculates and compares. If they differ, an error occurred and retransmission is requested. |
| Echo check | The received data is sent back to the sender and compared with the original. Weakness: you cannot tell whether the error occurred on the way there or on the way back. |
| Check digit | An extra digit calculated from the others, used on barcodes and ISBNs to catch typing and scanning errors. |
| Automatic Repeat reQuest (ARQ) | The receiver sends a positive or negative acknowledgement; if no acknowledgement arrives within a set time, the sender retransmits. |
A system uses even parity. The byte 1011001 is to be sent with a parity bit. What is the parity bit, and why?
- Count the 1s: 1, 1, 1, 1 → four 1s, which is already even
- Parity bit = 0, so the total number of 1s stays even
- If the receiver counts an odd number of 1s, it knows an error occurred during transmission.
2.3Encryption
| Symmetric encryption | Asymmetric encryption |
|---|---|
| The same key encrypts and decrypts | A public key encrypts and a matching private key decrypts |
| Faster; good for large volumes | Slower, but far more secure |
| Problem: the key must be sent to the recipient, and could be intercepted | The private key is never transmitted, so this problem disappears |
Hardware
3.1Computer architecture
The CPU processes instructions and data. In the Von Neumann architecture, data and instructions are both stored in the same memory, and instructions are fetched and executed one at a time.
| Component | Purpose |
|---|---|
| ALU (arithmetic logic unit) | Performs calculations and logical operations |
| CU (control unit) | Fetches, decodes and executes instructions; sends control signals |
| MAR (memory address register) | Holds the address of the memory location to be read from or written to |
| MDR (memory data register) | Holds the data just read from, or about to be written to, memory |
| PC (program counter) | Holds the address of the next instruction |
| ACC (accumulator) | Stores the result of calculations |
| Buses | Address bus (carries addresses, one direction), data bus (carries data, both directions), control bus (carries control signals) |
- The address in the PC is copied to the MAR.
- The instruction at that address is fetched into the MDR.
- The PC is incremented to point to the next instruction.
- The instruction is decoded by the control unit.
- The instruction is executed, with results stored in the accumulator.
Factors affecting CPU performance: clock speed (more cycles per second → more instructions), number of cores (more instructions processed simultaneously) and cache size (frequently used data held close to the CPU, so less waiting for slower RAM).
Embedded systems are computer systems built into a larger device to perform a dedicated task — washing machines, engine management, traffic lights. They are cheap, small, reliable and low-power, but usually hard to update and limited to one function.
3.2Input and output devices
Input devices (barcode scanner, QR scanner, digital camera, keyboard, microphone, touch screen, 2D/3D scanner) send data into the system. Output devices (monitor, printer, speaker, actuator, 3D printer) send data out.
Sensors are input devices that measure physical properties continuously — temperature, pressure, light, moisture, motion, infrared, gas, pH. Their analogue readings must be converted by an ADC before a computer can process them; a DAC converts digital signals back to analogue to drive actuators.
| Touch screen type | How it works | Notes |
|---|---|---|
| Resistive | Two conductive layers touch when pressed | Cheap; works with gloves or a stylus; poorer visibility; can be damaged by scratches |
| Capacitive | Detects change in the screen's electrical field from a finger | Good visibility and durability; supports multi-touch; does not work with ordinary gloves |
| Infrared | A grid of infrared beams is broken by a touch | Works with any object; affected by strong sunlight |
3.3Data storage
| RAM | ROM | |
|---|---|---|
| Volatile? | Volatile — contents lost when power is off | Non-volatile — contents kept |
| Can be written to? | Yes, read and write | Read only (in normal use) |
| Stores | Currently running programs, data and parts of the OS | Start-up instructions, e.g. the bootstrap/BIOS |
| Storage type | How it stores data | Examples |
|---|---|---|
| Magnetic | Magnetised sectors on spinning platters | Hard disk drive, magnetic tape — cheap per GB, large capacity, but moving parts can fail |
| Optical | A laser burns pits and lands on a reflective surface | CD, DVD, Blu-ray — cheap and portable, but small capacity and easily scratched |
| Solid state (SSD) | Control gates and floating gates trap electrons (no moving parts) | SSD, memory stick — fast, durable, silent, low power; more expensive per GB and a limited number of write cycles |
Virtual memory uses part of secondary storage as if it were RAM when RAM is full, allowing more programs to run — but it is much slower, causing "disk thrashing" if overused.
Cloud storage keeps data on remote servers accessed over the internet: accessible anywhere, no hardware to maintain, and backed up automatically — but it needs an internet connection, raises security and privacy concerns, and may incur ongoing costs.
3.4Network hardware
| Device | Function |
|---|---|
| NIC (network interface card) | Allows a device to connect to a network; holds the MAC address |
| MAC address | A unique hardware address for a device, in hexadecimal — normally fixed for the life of the device |
| IP address | Identifies a device on a network; can change (a static IP does not, a dynamic IP is reassigned) |
| Router | Connects networks and directs data packets between them using IP addresses |
IPv4 uses 32 bits written as four denary numbers (e.g. 192.168.0.1); IPv6 uses 128 bits written in hexadecimal, giving vastly more addresses because IPv4 is running out.
Software
4.1Types of software and interrupts
System software manages the computer (operating system, utilities, device drivers). Application software lets the user perform tasks (word processor, browser, spreadsheet).
Operating system tasks: managing files, managing memory, managing input/output devices, managing processes, providing a user interface, managing security and user accounts, and handling hardware/peripheral drivers.
4.2Languages, translators and IDEs
| High-level language | Low-level language (assembly/machine code) |
|---|---|
| Closer to English; easier to read, write and debug; portable across machines | Closer to machine code; specific to that processor |
| Must be translated before execution | Allows direct control of hardware; faster and more memory-efficient |
| Compiler | Interpreter | |
|---|---|---|
| Translates | The whole program at once into an executable file | One line at a time, executing as it goes |
| Errors | Reports all errors together at the end of compilation | Stops at the first error found |
| Speed | Runs faster once compiled; no translator needed to run it | Slower to run; the interpreter is needed every time |
| Best for | Finished, distributed software | Development and testing |
An IDE (integrated development environment) provides: code editing with syntax highlighting, error diagnostics and reports, auto-completion and auto-correction, prettyprinting (indentation and layout), and a built-in translator and debugger with breakpoints and single stepping.
Skill check: A developer is testing new code and wants errors reported as soon as each occurs. Which translator should they use, and why?
The internet and its uses
5.1The internet and the world wide web
URL structure: protocol (https), domain name, and file path. HTTP transfers web pages; HTTPS is the encrypted version, using SSL/TLS and a digital certificate so data cannot be read if intercepted.
Web browser functions: render HTML and display web pages, store bookmarks and history, allow multiple tabs, manage cookies, run JavaScript, and use a cache to load frequently visited pages faster.
Retrieving a web page: the browser sends the URL to a DNS server, which returns the matching IP address; the browser then requests the page from that web server, which sends back the HTML; the browser renders it.
Cookies are small text files storing user data. Session cookies are held in memory and lost when the browser closes; persistent cookies are saved to disk and remain — used to remember logins, preferences and shopping baskets.
5.2Digital currency
Digital currency exists only electronically and has no physical form. It relies on trust in the system, since there is no central bank issuing it.
5.3Cyber security
| Threat | What it does | Main protection |
|---|---|---|
| Brute-force attack | Tries every password combination until one works | Strong passwords, limited login attempts, two-step verification |
| Data interception | Packet sniffing to steal data in transit | Encryption, WPA on wireless |
| DDoS attack | Floods a server with requests so genuine users cannot access it | Firewall, proxy server |
| Hacking | Unauthorised access to a system | Firewalls, strong passwords, access levels |
| Malware | Virus, worm, trojan horse, spyware, adware, ransomware | Anti-malware software, not opening unknown attachments |
| Phishing | Fake emails trick users into revealing details | User awareness, spam filters, checking sender addresses |
| Pharming | Malicious code redirects the user to a fake website | Anti-malware, checking the URL and certificate |
| Social engineering | Manipulating people into breaking security procedures | Training and clear procedures |
Solutions to know: access levels, anti-malware, authentication (passwords, biometrics, two-step verification), automatic software updates, checking spelling and tone of communications, checking the URL, firewalls, privacy settings, and proxy servers.
Automated and emerging technologies
6.1Automated systems 6.2Robotics
Automated systems combine sensors, a microprocessor and actuators. The sensor reads data continuously, an ADC converts it, the microprocessor compares it with stored values, and if action is needed it signals an actuator (via a DAC) to respond — a continuous feedback loop.
Advantages: faster and more accurate than humans, works continuously without breaks, safer in hazardous environments, consistent quality, lower long-run labour costs. Disadvantages: expensive to install and maintain, job losses, vulnerable to faults and power failure, and inflexible if the task changes.
Robots have three characteristics: a mechanical structure, electrical components, and programmability. They may be independent (no human intervention) or dependent (needing a human interface). Used in industry, agriculture, medicine, domestic tasks, entertainment and exploration.
6.3Artificial intelligence
Expert systems have four parts: a knowledge base (facts), a rule base (IF–THEN rules), an inference engine (applies the rules to reach conclusions) and a user interface. They are used for medical diagnosis, mineral prospecting, financial planning and fault diagnosis.
Machine learning systems improve through experience by finding patterns in data rather than following only fixed rules.
Impacts: greater efficiency and access to expertise in remote areas, and the ability to work in dangerous settings — set against job displacement, high development cost, over-reliance on systems that can be wrong, and ethical concerns about bias and accountability.
Pseudocode reference
| Data type | Holds | Example |
|---|---|---|
| INTEGER | Whole numbers | 42 |
| REAL | Numbers with a decimal part | 3.75 |
| CHAR | A single character | 'A' |
| STRING | A sequence of characters | "Hello" |
| BOOLEAN | TRUE or FALSE | TRUE |
Algorithm design and problem-solving
7Algorithm design and problem-solving
Program development life cycle: analysis → design → coding → testing. Decomposition breaks a problem into inputs, processes and outputs; abstraction keeps only the details that matter and removes the rest.
Algorithms can be expressed as structure diagrams, flowcharts or pseudocode.
| Flowchart symbol | Meaning |
|---|---|
| Oval (terminator) | Begin / End |
| Parallelogram | Input / Output |
| Rectangle | Process |
| Diamond | Decision |
| Arrow | Flow of control |
Test data types: normal (accepted and typical), abnormal/erroneous (should be rejected), extreme (at the limits of acceptability) and boundary (the largest accepted value and the smallest rejected value, or vice versa).
| Count | Total | OUTPUT |
|---|---|---|
| — | 0 | |
| 1 | 1 | |
| 2 | 3 | |
| 3 | 6 | |
| 4 | 10 | 10 |
Standard methods you must know: a linear search (check each item in turn until found or the list ends), a bubble sort (repeatedly compare adjacent items and swap if out of order until a pass makes no swaps), and using totalling, counting, finding maximum, minimum and average.
Write an algorithm that repeatedly asks for a mark until a valid mark between 0 and 100 is entered.
This is a range check. A WHILE loop is right because a valid first entry should not trigger the error message at all.
Skill check: For a range check accepting 1–50, give one item of normal, abnormal, extreme and boundary test data.
Programming
8.1Programming concepts
The three programming constructs: sequence (statements in order), selection (IF / CASE) and iteration (FOR / WHILE / REPEAT). Every algorithm is built from these.
| Operator group | Operators |
|---|---|
| Arithmetic | + − * / ^ DIV (integer division) MOD (remainder) |
| Comparison | = <> < <= > >= |
| Logical | AND OR NOT |
Evaluate 17 DIV 5 and 17 MOD 5, and explain a use for MOD.
- 17 DIV 5 = 3 (the whole number of times 5 goes into 17)
- 17 MOD 5 = 2 (the remainder)
- MOD is commonly used to test divisibility: if N MOD 2 = 0 then N is even.
Library routines you should know: MOD, DIV, ROUND, RANDOM. Procedures and functions break a program into manageable named sub-programs — the key difference is that a function returns a value and a procedure does not. Both may take parameters. Benefits: code can be reused, is easier to test and debug, and several people can work on different modules.
8.2Arrays
An array stores multiple values of the same data type under one identifier, accessed by index. A 1D array is a list; a 2D array is a table with rows and columns.
8.3File handling
Files provide persistent storage — data survives after the program ends, unlike variables. You must be able to open a file for reading or writing, read from and write to it, and always close it afterwards.
Databases
9Databases
| Data type | Use for |
|---|---|
| Text/alphanumeric | Names, addresses, codes containing letters |
| Character | A single letter or symbol |
| Boolean | Yes/No, True/False fields |
| Integer | Whole numbers — quantities, ages |
| Real | Numbers with decimals — prices, measurements |
| Date/time | Dates and times |
From a table Stock with fields ItemID, ItemName, Price and Quantity, write SQL to list the name and price of all items costing more than 50, sorted from most to least expensive.
To count how many items are in stock: SELECT COUNT(ItemID) FROM Stock
Skill check: Write SQL to show all fields for students in class '10A', sorted by surname alphabetically, from a table called Students.
SELECT *
FROM Students
WHERE Class = '10A'
ORDER BY Surname ASC
Boolean logic
10Boolean logic
| Gate | Behaviour | Truth table (A, B → output) |
|---|---|---|
| NOT | Output is the opposite of the input | 0→1, 1→0 |
| AND | Output 1 only if both inputs are 1 | 00→0, 01→0, 10→0, 11→1 |
| OR | Output 1 if either or both inputs are 1 | 00→0, 01→1, 10→1, 11→1 |
| NAND | NOT AND — output 0 only if both inputs are 1 | 00→1, 01→1, 10→1, 11→0 |
| NOR | NOT OR — output 1 only if both inputs are 0 | 00→1, 01→0, 10→0, 11→0 |
| XOR | Output 1 if the inputs are different | 00→0, 01→1, 10→1, 11→0 |
- List every input combination — 2n rows for n inputs (3 inputs = 8 rows).
- Add a column for each intermediate gate output, working left to right through the circuit.
- Complete the final output column last.
Complete the truth table for X = (A AND B) OR (NOT C).
| A | B | C | A AND B | NOT C | X |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 1 | 1 |
| 0 | 0 | 1 | 0 | 0 | 0 |
| 0 | 1 | 0 | 0 | 1 | 1 |
| 0 | 1 | 1 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 1 | 1 |
| 1 | 0 | 1 | 0 | 0 | 0 |
| 1 | 1 | 0 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 0 | 1 |
Logic expressions from a scenario are a standard question: read each condition carefully and decide whether it needs AND (both must be true), OR (either), or NOT (the opposite). "An alarm sounds if the door is open AND the system is armed, OR if the panic button is pressed" becomes X = (D AND S) OR P.
Skill check: A heater turns on (X = 1) when the temperature sensor reads below 18 °C (T = 0 means below) and the system is switched on (S = 1). Write the logic expression.
Study planner & progress
Every syllabus unit. Tick one when you can answer a past-paper question on it unaided. Your ticks are saved on this device only — nothing is sent anywhere, and there is no account to create.
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Free past papers & how to revise
Official (free)
- Cambridge International — 2210 subject page: syllabus, specimen papers, past papers, mark schemes and examiner reports.
- Examiner reports name the exact questions candidates got wrong each series — read them for every paper you attempt.
Free archives
- GCE Guide · PastPapers.co — full CAIE past-paper archives.
- Physics & Maths Tutor — topic-sorted questions.
How to revise this subject
- Drill number conversions daily until they are automatic without a calculator — binary ↔ denary ↔ hexadecimal. They appear on Paper 1 every series.
- Write pseudocode by hand. Typing in an IDE does not prepare you for hand-writing correct syntax under time pressure.
- Practise trace tables line by line. Do not skip steps mentally — write every value change, including the final loop check.
- Learn definitions precisely. Paper 1 rewards exact terminology: "validation" vs "verification", "compiler" vs "interpreter", "RAM" vs "ROM".
- For every hardware/software topic, learn one clear purpose plus one advantage or drawback — that is the usual shape of a 2–3 mark question.