Binary Place Values
Bits from left to right represent 2ⁿ down to 2⁰.
Decimal = Σ (bit × 2^position) Pearson Edexcel International GCSE 4CP0
💻 Edexcel IGCSE Computer Science Formula Sheet 2025
Key binary, logic, storage, CPU, and networking calculations for Edexcel IGCSE theory (Paper 1) and practical programming (Paper 2).
Binary & Hex Logic Gates Data Storage Networking
Your Quick-Reference Guide for Edexcel CS Calculations
Use this cheat sheet alongside pseudocode practice to stay confident with conversions, data size estimates, and performance calculations that Edexcel loves to assess.
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Binary ↔ decimal ↔ hexadecimal conversions
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Boolean algebra and logic gate reminders
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Storage, sound, and image file calculations
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CPU timing, bandwidth, and latency formulas
Number Bases & Conversions
Decimal to Binary
Repeatedly divide by 2, record remainders, read remainders in reverse.
Binary to Hexadecimal
Group binary digits into nibbles (4 bits) from the right and convert each nibble to hex.
Two’s Complement
Invert bits (one’s complement) then add 1 to represent negative numbers.
Binary Addition Rules
0 + 0 = 0 (carry 0) 0 + 1 = 1 (carry 0) 1 + 1 = 0 (carry 1) 1 + 1 + 1 = 1 (carry 1) Data Representation & Storage
Units
1 nibble = 4 bits, 1 byte = 8 bits, 1 KB = 1024 bytes, 1 MB = 1024 KB, etc.
Text Files
ASCII uses 7/8 bits; Unicode (UTF-16) uses 16 bits per character.
File size (bits) = Number of characters × Bits per character Bitmap Images
Colour depth bits per pixel; divide by 8 for bytes.
File size (bits) = Width × Height × Colour depth File size (bytes) = (Width × Height × Colour depth) / 8 Sound Files
Sample rate in Hz (samples per second), bit depth bits per sample.
File size (bits) = Sample rate × Bit depth × Duration × Number of channels Video Estimate
Frame size × frame rate × duration (apply compression factor if given).
File size (bits) ≈ Frame size × Frame rate × Duration Logic Gates & Boolean Algebra
Gate Outputs
A, B inputs (0 or 1). ¬ = NOT, · = AND, + = OR.
NOT A = ¬A AND: A · B OR: A + B NAND: ¬(A · B) NOR: ¬(A + B) XOR: A ⊕ B De Morgan’s Laws
¬(A · B) = ¬A + ¬B ¬(A + B) = ¬A · ¬B Half Adder
Use for binary addition in exam logic design questions.
Sum = A ⊕ B Carry = A · B CPU Performance & Networking
CPU Timing
Clock speed in Hz (cycles/s), CPI cycles per instruction.
Time per cycle = 1 / Clock speed Execution time = Number of cycles × Time per cycle Bandwidth & Data Transfer
Measure file size in bits for transmission calculations.
Bandwidth (bps) = Data transferred / Time Transmission time = File size (bits) / Transmission rate (bits per second) Latency Components
Latency ≈ propagation + transmission + processing delay.
Bit Rate vs Baud Rate
Bit rate = baud rate × bits per symbol (binary: equal values).
Algorithms & Pseudocode Reminders
Linear vs Binary Search
Binary search comparisons ≈ ⌈log₂ n⌉ where n is list length.
Average Calculation
Remember to initialise total ← 0, count ← 0.
average ← total / count Complexity Notation
Know typical orders: bubble sort O(n²), merge sort O(n log n), binary search O(log n).
Verification vs Validation
Validation = range, length checks; verification = double entry/visual check.
How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Show Working in Base Changes
Write each step in conversions to gain method credit even if a digit slips.
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Annotate Pseudocode
Add short comments describing purpose of loops and variables, especially under time pressure.
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Connect Calculations to Hardware
Explain what a higher bandwidth, latency, or CPI means for the real scenario in long answers.
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Recreate Tables from Past Papers
Practice converting entire truth tables, ASCII charts, and check digit examples to build speed.
Power Up Your Edexcel CS Revision
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Aligned with Pearson Edexcel International GCSE Computer Science (4CP0) specification calculations.
Always state units (bits, bytes, Hz, seconds) and show intermediate steps for top marks.