Von Neumann Architecture
Single shared memory and bus for instructions and data | CPU contains CU, ALU and registers OCR GCSE Computer Science J277
💻 OCR GCSE Computer Science Formula Sheet 2026
Every essential formula and definition for OCR J277 — systems architecture, memory & storage calculations, networks, algorithms, programming, Boolean logic and data representation.
Computer Systems Algorithms Programming Data Representation
Our formula sheets are free to download — save this one as PDF for offline revision.
Aligned with the latest 2026 syllabus and board specifications. This sheet is prepared to match your exam board’s official specifications for the 2026 exam series.
All the OCR GCSE Computer Science Essentials in One Sheet
OCR GCSE Computer Science (J277) tests both Component 1 (Computer Systems) and Component 2 (Computational Thinking, Algorithms & Programming). This formula sheet brings together every key calculation, definition and rule across both papers for fast 2026 revision.
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Systems architecture, memory and storage calculations
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Networks, protocols and security threats
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Algorithms, searches and sorts with complexity
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Boolean logic and binary/hex data representation
1.1 Systems Architecture
How the CPU executes instructions.
Fetch-Decode-Execute Cycle
Fetch
PC → MAR; instruction copied to MDR; PC incremented Decode
CU decodes instruction in CIR Execute
ALU performs operation; result stored in accumulator/register Registers
PC (Program Counter) | MAR (Memory Address Register) | MDR (Memory Data Register) | CIR (Current Instruction Register) | ACC (Accumulator) Factors Affecting CPU Performance
Clock speed
Hz — instructions per second; higher = faster but more heat/power Cache size
Larger cache = fewer slow RAM fetches Number of cores
More cores = more instructions in parallel (if software supports it) 1.2 Memory & Storage Calculations
Capacity calculations are guaranteed exam content.
RAM, ROM & Virtual Memory
RAM
Volatile, read/write, holds running programs and data ROM
Non-volatile, read-only, holds bootloader / firmware Virtual memory
Section of secondary storage used as RAM when RAM is full — slower Secondary Storage
Magnetic (HDD) | Optical (CD/DVD/Blu-ray) | Solid-state (SSD/USB) — compare on capacity, speed, durability, cost, portability File Size — Images
Image file size
Size = Width × Height × Bit depth ÷ 8 (bytes); add header where applicable Bit depth: 1-bit = 2 colours; 8-bit = 256 colours; 24-bit = 16.7M colours
File Size — Sound
Sound file size
Size = Sample rate × Sample resolution (bit depth) × Duration (s) ÷ 8 (bytes) Higher sample rate / bit depth → better quality but larger file Units of Storage
1 byte = 8 bits | 1 KB = 1000 bytes | 1 MB = 1000 KB | 1 GB = 1000 MB | 1 TB = 1000 GB | 1 PB = 1000 TB 1.3 Networks & Security
From topologies to threats and encryption.
Network Types & Topologies
LAN (single site) vs WAN (across multiple sites; Internet is largest WAN) Topologies: Star (central switch — robust) | Mesh (every node connected — resilient) Protocols
Web
HTTP / HTTPS (secure) | TCP/IP (transport + network) | FTP (file transfer) SMTP (sending) | POP / IMAP (receiving — IMAP keeps a server copy) Packet Switching
Data split into packets, each routed independently, reassembled at destination | Includes header (addresses, sequence) + payload Security Threats
Malware (virus, worm, trojan, ransomware, spyware) | Social engineering (phishing, pretexting, shoulder surfing) Brute-force attacks | Denial-of-service (DoS / DDoS) | SQL injection | Data interception Defences
Encryption | Strong passwords + 2FA | Firewalls | Anti-malware | User access levels | Penetration testing | Physical security 1.4 & 1.5 Systems Software, Ethics & Law
Operating systems and the wider impact of computing.
Operating System Functions
User interface | Memory management | Process / multitasking management | Peripheral / device driver management | File management | User account management Utility Software
Encryption | Defragmentation | Data compression | Backup | Anti-malware Ethical, Legal & Cultural Issues
Data Protection Act (2018) | Computer Misuse Act (1990) | Copyright, Designs and Patents Act (1988) | Software licensing (open source vs proprietary) Issues: privacy, automation, digital divide, environmental impact, cyberbullying 2.1 Algorithms
Computational thinking, searches and sorts.
Computational Thinking
Abstraction
Removing unnecessary detail to focus on the problem Decomposition
Breaking a problem into smaller, manageable subproblems Algorithmic thinking
Designing a step-by-step solution (often using flowcharts or pseudocode) Searching
Linear search
Check each element in turn — works on unordered lists | O(n) Binary search
Halve a sorted list each step using the midpoint | O(log n) Sorting
Bubble sort
Repeatedly swap adjacent out-of-order pairs | Simple, slow, O(n²) Insertion sort
Build sorted list by inserting each new element into the right place | O(n²) but fast for nearly sorted Merge sort
Divide and conquer — split, recursively sort halves, merge | O(n log n) Trace Tables
Columns = variables (and outputs) | Rows = each iteration / line execution | Used to dry-run algorithms and find errors 2.2 & 2.3 Programming Techniques
From data types to robust programs.
Programming Constructs
Sequence
Statements run one after another Selection
if / elif / else — branch on Boolean conditions Iteration
Count-controlled (for) | Condition-controlled (while) Data Types & Structures
Integer | Real / Float | Boolean | Character | String 1D arrays: list[i] | 2D arrays: list[row][col] | Records (multiple fields per item) Subroutines
Procedures
Perform a task without returning a value Functions
Return a value to the caller Benefits: reuse, abstraction, easier testing and maintenance File Handling & SQL
Open file → read / write / append → close file SQL
SELECT <fields> FROM <table> WHERE <condition> Defensive Design & Testing
Validation: range, type, presence, length, format checks Authentication, anticipating misuse, contingency planning, maintainability (comments, indentation, meaningful names, modularisation) Iterative testing throughout development | Final / terminal testing before release Test data: normal | boundary | invalid / erroneous 2.4 Boolean Logic
Gates, expressions and truth tables.
Logic Gates & Operators
AND
A · B = 1 only when both A and B are 1 OR
A + B = 1 if A or B (or both) are 1 NOT
¬A = 1 when A = 0 (and vice versa) Truth Tables
Number of rows = 2ⁿ for n inputs | Build column by column for sub-expressions, then combine Boolean Expressions
Combine AND, OR, NOT — e.g. Q = A · ¬B + C — read as 'A and not B, or C' 2.5 Languages, Translators & Data Representation
Final sweep — high/low level languages, IDEs, binary and characters.
Languages & Translators
High-level (Python, Java) — easier to read/write, machine-independent | Low-level (assembly, machine code) — fast, hardware-specific Compiler
Translates entire program before execution; fast at runtime; harder to debug Interpreter
Translates and executes line by line; slower runtime; easier debugging Assembler
Translates assembly language into machine code Binary, Hex & Two's Complement
Binary place values: 128 64 32 16 8 4 2 1 (8-bit byte) Hex digits: 0–9, A–F (A = 10, F = 15) | Each hex digit = 4 binary bits Two's complement (8-bit)
Negative: invert all bits, add 1 — MSB is sign bit Binary addition
0+0=0 | 0+1=1 | 1+1=10 | 1+1+1=11 (carry) Binary shift
Left by n = ×2ⁿ | Right by n = ÷2ⁿ Character Encoding
ASCII
7-bit (128 chars) or extended 8-bit (256 chars) — covers Latin alphabet and basic symbols Unicode
16-bit and beyond — supports thousands of characters across all global scripts How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Drill the Calculations
Image and sound file size questions appear most years — practise until you can do them in under a minute, including unit conversions.
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Trace Algorithms by Hand
Use trace tables for searches, sorts and unfamiliar pseudocode — examiners reward clean line-by-line working.
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Master Binary & Hex
Convert between binary, hex and denary daily. Add binary numbers, perform shifts, and practise two's complement for negatives.
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Code Little and Often
Write small Python programs each week — selection, iteration, arrays, file handling and SQL queries — to consolidate Component 2 content.
Formula Sheet FAQ
Quick answers about this free PDF and how to use it for exam revision and active recall.
Is the OCR GCSE Computer Science Formula Sheet 2026 free to download as a PDF?
Yes. This Tutopiya formula sheet is free to use and you can download it as a PDF from this page for offline revision. There is no payment or account required for the PDF download.
What Computer Science topics and equations does this formula sheet cover?
This page groups key Computer Science formulas in one place for revision. Master OCR GCSE Computer Science (J277) with this 2026 formula sheet. Covers systems architecture, memory & storage, networks, algorithms, programming, Boolean logic and data representation. Always cross-check with your official syllabus and past papers for your exam session.
Can I use this instead of the official exam formula booklet in the exam?
No. In the exam you must follow only what your exam board allows in the hall—usually the official formula booklet or data sheet where provided. This page is a revision and teaching aid, not a replacement for board-issued materials.
Who is this formula sheet for (Secondary)?
It is written for students preparing for assessments at Secondary in Computer Science, including classroom revision, homework support, and independent study. Teachers and tutors can also share it as a quick reference.
How should I revise with this formula sheet?
Work through past paper questions, quote the correct formula before substituting values, and check units and notation every time. Pair this sheet with timed practice and mark schemes so you see how examiners expect working to be set out.
Where can I get more help with Computer Science revision?
Explore Tutopiya’s study tools, past paper finder, and revision checklists linked from our tools hub, or book a trial lesson with a subject specialist for personalised support alongside this formula reference.
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This formula sheet aligns with OCR GCSE Computer Science (J277) 2026 syllabus content across Components 1 and 2.
Always show working for file size, binary and trace table questions — OCR rewards method even when the final answer is wrong.