Key Terms
- Bit: The smallest unit of data — a single binary digit, either 0 or 1
- Byte: 8 bits — enough to store one character (e.g. the letter 'A')
- Kilobyte (KB): 1,024 bytes
- Megabyte (MB): 1,024 KB
- Gigabyte (GB): 1,024 MB
- Terabyte (TB): 1,024 GB
- Petabyte (PB): 1,024 TB
Must-Know Facts
- 1 byte = 8 bits (always — never changes)
- Each unit is 1,024 times the previous (NOT 1,000) because computers use binary (powers of 2)
- Convert GB → MB: multiply by 1,024; convert MB → GB: divide by 1,024
- Bits (lowercase b) measure transmission speed; Bytes (uppercase B) measure file/storage size
- To convert Mbps to MB/s: divide by 8 (e.g. 100 Mbps ÷ 8 = 12.5 MB/s)
- Using 1,000 instead of 1,024 is incorrect in binary calculations
Key Concepts
- Storage ladder: bit → byte (×8) → KB (×1,024) → MB (×1,024) → GB (×1,024) → TB (×1,024)
- Real-world sizes: 1 KB ≈ short email; 1 MB ≈ photo; 1 GB ≈ HD film; 1 TB ≈ 250 films
- File count calculation: total storage ÷ file size = number of files (convert to same units first)
- Calculation strategy: identify units → convert to same unit → choose × or ÷ → show working
Common Mistakes
- Using 1,000 instead of 1,024: In binary/computing, 1 KB = 1,024 bytes (not 1,000) — always use powers of 2 in exam calculations
- Forgetting to convert units before calculating: If a file is given in MB and storage is given in GB, convert to the same unit first before dividing to find how many files fit
- Confusing bits and bytes: 1 byte = 8 bits — internet speeds are often quoted in bits per second (Mbps) while file sizes are in bytes (MB), so always check which unit is being used
- Saying a nibble is 4 bytes: A nibble is 4 bits (half a byte), not 4 bytes — the order is: nibble (4 bits) < byte (8 bits) < KB < MB < GB
This topic summary covers Knowledge Organiser: Storage Units within Storage Units for GCSE Computer Science. Revise Storage Units in 3.3 Data Representation for GCSE Computer Science with 15 exam-style questions and 18 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 10 of 10 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Storage Units
How many bits make up one nibble?
Explain what is meant by colour depth and describe how increasing the colour depth affects both the image quality and the file size.