💻 Edexcel IGCSE Computer Science Formula Sheet 2026

Binary Place Values

Bits from left to right represent 2ⁿ down to 2⁰.

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

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.

Bitmap Images

Colour depth bits per pixel; divide by 8 for bytes.

Sound Files

Sample rate in Hz (samples per second), bit depth bits per sample.

Video Estimate

Frame size × frame rate × duration (apply compression factor if given).

Gate Outputs

A, B inputs (0 or 1). ¬ = NOT, · = AND, + = OR.

De Morgan’s Laws

Half Adder

Use for binary addition in exam logic design questions.

CPU Timing

Clock speed in Hz (cycles/s), CPI cycles per instruction.

Bandwidth & Data Transfer

Measure file size in bits for transmission calculations.

Latency Components

Latency ≈ propagation + transmission + processing delay.

Bit Rate vs Baud Rate

Bit rate = baud rate × bits per symbol (binary: equal values).

Linear vs Binary Search

Binary search comparisons ≈ ⌈log₂ n⌉ where n is list length.

Average Calculation

Remember to initialise total ← 0, count ← 0.

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.