Bytes, Kilobytes, Megabytes, Gigabytes — Data Storage Explained

Everyone uses gigabytes daily but most people couldn't explain exactly how many megabytes are in one. Here's a clear breakdown of data storage units and the maddening SI vs binary divide.

The byte is the fundamental unit of digital data — a single byte contains 8 bits, and a bit is the smallest possible unit of binary information, a single 0 or 1. Everything from a text message to a 4K film is ultimately measured in bytes.

The confusion in data storage measurements comes from two competing standards. The traditional computer science standard defines a kilobyte as 1,024 bytes (2¹⁰), a megabyte as 1,024 kilobytes (2²⁰), and so on — using powers of two, which is natural for binary computing. The SI (International System of Units) standard defines a kilobyte as exactly 1,000 bytes, a megabyte as exactly 1,000,000 bytes, and so on.

Hard drive manufacturers use the SI definition (1GB = 1,000,000,000 bytes) because it makes their drives appear larger. Operating systems traditionally used the binary definition (1GB = 1,073,741,824 bytes) because that's how memory is actually addressed. The result: a hard drive advertised as 1TB contains 1,000,000,000,000 bytes, but your operating system might report it as 931GB because it's dividing by 1,073,741,824 instead of 1,000,000,000.

The IEC introduced new prefixes to eliminate this ambiguity: a kibibyte (KiB) is exactly 1,024 bytes, a mebibyte (MiB) is exactly 1,048,576 bytes, and a gibibyte (GiB) is exactly 1,073,741,824 bytes. Most operating systems have slowly adopted these — macOS reports storage in GB (using SI), while Linux and Windows have been more variable.