the amount of storage available on a hard disk drive is measured in
Hard disk drive The total capacity of HDDs is given by manufacturers using SI decimal prefixes such as gigabytes (1 GB = 1,000,000,000 bytes) and terabytes (1 TB = 1,000,000,000,000 bytes).[91] This practice dates back to the early days of computing;[93] by the 1970s, "million", "mega" and "M" were consistently used in the decimal sense for drive capacity.[94][95][96] However, capacities of memory are quoted using a binary interpretation of the prefixes, i.e. using powers of 1024 instead of 1000.