Binary Prefixes
1. The Two Standards
Historically, the term "Kilobyte" was used to mean 1024 bytes. However, to stay consistent with scientific SI units, the IEC (International Electrotechnical Commission) introduced specific Binary Prefixes.
Metric (SI) Units
Based on Powers of 10. Used by drive manufacturers and in networking.
103 = 1,000
Example: Kilobyte (kB)
Binary (IEC) Units
Based on Powers of 2. Used by Operating Systems and for RAM.
210 = 1,024
Example: Kibibyte (KiB)
2. The Binary Prefix Table
For the IGCSE exam, you must use the 1024-based names when referring to memory sizes.
| Unit Name | Abbreviation | Value (Bytes) | Power of 2 |
|---|---|---|---|
| Kibibyte | KiB | 1,024 | 210 |
| Mebibyte | MiB | 1,048,576 | 220 |
| Gibibyte | GiB | 1,073,741,824 | 230 |
| Tebibyte | TiB | 1,099,511,627,776 | 240 |
| Pebibyte | PiB | 1,125,899,906,842,624 | 250 |
3. Smallest Units of Data
- Bit: A single 0 or 1. (Short for Binary Digit).
- Nibble: A group of 4 bits.
- Byte: A group of 8 bits. (The standard unit for one character of text).
4. Conversion Formulas
Exam Tip: When calculating data sizes, always multiply or divide by 1024, not 1000.
| Smaller to Larger | Larger to Smaller |
| Divide by 1024 | Multiply by 1024 |
| (e.g., KiB to MiB) | (e.g., GiB to MiB) |
Example Calculation:
How many MiB are in 2 GiB?
$2 \times 1024 = 2048 \text{ MiB}$