The terabyte, unit of digital data

The terabyte is 1000 gigabytes, that is 10¹² bytes, written TB. One terabyte holds about 250 000 photographs of 4 MB, which is why it became the ordinary size of a home disk.

The terabyte is the scale at which the two ways of counting become impossible to ignore. A disk sold as 1 TB holds a thousand billion bytes; an operating system that divides by 1024 three times calls the same disk 931, and the 69 that seem to vanish are not missing space but the same bytes under a second name. The gap widens with the size because it is a ratio and not a fixed subtraction: 2 TB reads 1863, 4 TB reads 3725, 8 TB reads 7451, always the same 7.4 per cent. The binary quantity has had its own name since 1998, the tebibyte, symbol TiB.

The terabyte in other units

Digital storage