Six units. Every specification checkpoint. Explore how computer systems work, test your understanding and prepare for Paper 1.
15 TOPICS127 KNOWLEDGE CHECKS144 PRACTICE QUESTIONSOFFLINE READY
01
INSIDE THE SYSTEM
J277/01 · COMPUTER SYSTEMS
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THE COMPLETE PAPER 1 EXPLORER
Learn the system. Master the exam.
Choose a topic, follow illustrated explanations, mark each specification requirement as confident or needs practice, then test yourself.
OCR J277/01 · VERSION 3.1 · MAY 2026
Computer systems
Paper 1 focuses on systems architecture, storage, networking, security, systems software and the impacts of technology. This guide follows the six content areas of the official specification.
Step through one conceptual CPU instruction. Follow how the CPU fetches, interprets and carries out an operation.
1 · FETCH
2 · DECODE
3 · EXECUTE
01
Binary & hex workbench
1.2.4 · REPRESENTATION
Explore every bit in an 8-bit number. Practise denary/binary/hex conversion, addition and logical shifts.
00101101
128 64 32 16 8 4 2 1 · click any bit to toggle it
Try it · Binary / hex conversion
Type your answer and check it. After any attempt, you can move to the next question even if your answer is incorrect. Incorrect answers do not reveal the solution.
Addition result (8-bit limit)
145
No overflow
Try it · Binary addition
Work from right to left. Type 1 in every carry box that receives a carry (including the far-left overflow box when needed), and leave the other carry boxes blank. Enter each bit of the 8-bit answer in the bottom row. Both rows must be right to complete the question.
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File size calculator
1.2.3–1.2.4 · STORAGE, IMAGES, AUDIO
Model an uncompressed file using the specification formulas. Calculations here use decimal units (1 KB = 1,000 bytes).
WIDTH × HEIGHT × COLOUR DEPTH
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Adjust the values to see the calculation.
Try it · File size calculations
Work out each uncompressed size without using the live calculator. Type the numeric answer in the unit requested. All questions use decimal units where relevant.
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Network decision lab
1.3.1–1.3.2 · NETWORKS
Pick the best hardware, medium or protocol for each situation. Try again if your answer is incorrect; only a correct choice is highlighted green.
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Security response lab
1.4.1–1.4.2 · THREATS & DEFENCES
Recognise an attack and decide which safeguard directly addresses it. Try again if your answer is incorrect; only a correct choice is highlighted green.
48 NEW EXAM-STYLE QUESTIONS
Additional topic challenges
Check your answer to unlock Next, even if it is incorrect. Solutions are not revealed after incorrect attempts, and you can return to retry questions using Previous.
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Binary shift challenge
1.2.4 · MEMORY & STORAGE
Use an 8-bit unsigned number. Shift bits to the left or right, insert zeros into empty positions and discard bits moved outside the eight positions.
Revision note A left shift doubles the value for each place only if no significant bit is lost. A right shift discards any remainder.
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Storage units & capacity
1.2.3 · MEMORY & STORAGE
Convert between storage units and work out simple capacity requirements. Use decimal multiples: 1 KB = 1,000 bytes, 1 MB = 1,000 KB.
Revision note 1 nibble = 4 bits; 1 byte = 8 bits. OCR also accepts 1,024-based conversions when clearly used, but these questions explicitly use 1,000.
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Characters, pixels & audio
1.2.4 · MEMORY & STORAGE
Apply how bit depth, resolution, sampling and character sets change what can be represented and the amount of storage required.
Revision note A character set with n bits can represent 2ⁿ different bit patterns. For images, increasing pixel count or colour depth usually increases uncompressed file size.
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CPU registers & performance
1.1.1–1.1.2 · SYSTEMS ARCHITECTURE
Identify what each Von Neumann register holds and use CPU performance characteristics to reason about real scenarios.
Revision note Decide whether each register holds an address, data, or an arithmetic result. Some performance improvements depend on the workload.
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Primary & secondary storage
1.2.1–1.2.2 · MEMORY & STORAGE
Choose between RAM, ROM, cache, virtual memory and secondary-storage media based on cost, speed, capacity, durability and purpose.
Revision note RAM is normally volatile, ROM is non-volatile, and secondary storage is needed to keep files and programs when power is switched off.
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Compression decisions
1.2.5 · MEMORY & STORAGE
Choose lossy or lossless compression for different scenarios and describe what happens to the original data.
Revision note Lossless compression reconstructs the original data exactly; lossy compression permanently removes some information for potentially smaller files.
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Protocols & addressing
1.3.2 · NETWORKS & CONNECTIONS
Identify protocol purposes and recognise network address formats. Focus on their role, not on unrequired detailed protocol mechanisms.
Revision note Work from each protocol’s purpose and the scenario. For addresses, distinguish a device-interface identifier from a network address.
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Operating systems, laws & licences
1.5–1.6 · SYSTEMS SOFTWARE & IMPACTS
Apply operating-system and utility functions, legislation and licence choices to practical scenarios.
Revision note Legal questions are about what the named law protects or prohibits. Licence questions need a justified choice and awareness of trade-offs.
EXAM BOUNDARY
The models here are simplified. For example, the actual CPU has more internal detail than the three steps shown; the OCR exam does not require knowing every transfer between registers. The file estimator ignores headers/metadata unless provided in a question.
ASSESS YOUR UNDERSTANDING
Knowledge check
Original practice questions across all 15 subtopics. Choose a focus and get immediate, explained feedback. This is a revision tool, not an official OCR past paper.
Clears quiz and lab responses only; your specification checklist stays as it is.
YOUR SPECIFICATION MAP
Every requirement. One checklist.
Use Not yet, Needs work or Confident for each learning objective. Progress is saved on this device in your browser; “Confident” is your self-assessment, not an exam grade.
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Confident checkpoints
0 flagged for revision
Important: boundaries — things OCR says are not required
EXTENDED RESPONSE PRACTICE
Think like an examiner
Try each original applied-response prompt before revealing the indicative points. Answer in full sentences and explain each idea in context. These are practice prompts, not official mark schemes.
1.1.1
Write your answer on paper first. Explain causes/effects and apply your reasoning to the scenario. Then reveal the indicative response points.