The big idea
Computers store everything as bits (binary digits, 0 or 1). People prefer denary (base 10), and programmers often use hexadecimal (base 16) as a short way to write binary. At A Level you need to move between all three quickly and by hand, because there are no calculators in the exam. You also need to be precise about sizes: a "kilobyte" and a "kibibyte" are not the same thing.
Explained simply
Decimal prefixes come from the metric system and go up in powers of 10. Binary prefixes were introduced so that sizes built from powers of 2 have their own exact names.
| Decimal prefix | Value | Binary prefix | Value |
|---|---|---|---|
| kilo (kB) | kibi (KiB) |