Digital data is stored as binary digits (bits); 8 bits = 1 byte. Two prefix systems create persistent confusion: SI decimal prefixes (1 KB = 1,000 bytes, used by hard drive manufacturers and network speeds) versus binary prefixes (1 KiB = 1,024 = 2¹⁰ bytes, used by operating systems for RAM and file sizes). A 1 TB hard drive (10¹² bytes by manufacturer specification) appears as about 931 GiB in Windows — because Windows uses binary-based units but historically mislabelled them "GB".
The IEC standardised binary prefixes (KiB, MiB, GiB, TiB, PiB) in 1998 to resolve this ambiguity, but operating system adoption has been inconsistent. Network speeds are always measured in bits per second, not bytes: a 100 Mbps connection transfers approximately 12.5 MB/s. When calculating how long a file download takes, always divide the file size in megabytes by 8 before dividing by the connection speed in megabits.
| 1 byte | = 8 bits |
| 1 KB | = 1,000 bytes |
| 1 KiB | = 1,024 bytes |
| 1 GB | = 10⁹ bytes |
| 1 GiB | = 1,073,741,824 bytes |
| 1 TB | = 10¹² bytes |
| 1 TiB | = 2⁴⁰ bytes |