The gigabyte, unit of digital data

The gigabyte is 1000 megabytes, that is one billion bytes, written GB. A dual layer DVD holds 8.5 gigabytes and a Blu-ray disc 25, while a mobile plan is now counted in tens of them.

The same three letters name two different quantities inside one machine. Memory is addressed in powers of two, so a 16 GB module really holds sixteen times 2³⁰ bytes and the label is exact; a disk sold as 1 TB holds 10¹² bytes, counted in thousands, and its label is exact too. The two conventions differ by 7.4 per cent at this scale, which is why the operating system shows less than the box promised on the disk and exactly what the box promised on the memory. The IEC gave the binary quantity its own name in 1998, the gibibyte, symbol GiB, and the industry kept writing GB for both.

The gigabyte in other units

Digital storage