Thats the way formatting works.
The total capacity of HDDs is given by manufacturers in megabytes (1 MB = 1,000,000 bytes), gigabytes (1 GB = 1,000,000,000 bytes) or terabytes (1 TB = 1,000,000,000,000 bytes).[41][43][44][45][46][47] This numbering convention, where prefixes like mega- and giga- denote powers of 1,000, is also used for data transmission rates and DVD capacities. However, the convention is different from that used by manufacturers of memory (RAM, ROM) and CDs, where prefixes like kilo- and mega- mean powers of 1,024.
The practice of using prefixes assigned to powers of 1,000 within the HDD and computer industries dates back to the early days of computing.[48] By the 1970s million, mega and M were consistently being used in the powers of 1,000 sense to describe HDD capacity.[49][50][51]
Computers do not internally represent HDD or memory capacity in powers of 1,024; reporting it in this manner is just a convention.[52]Microsoft Windows uses the powers of 1,024 convention when reporting HDD capacity, thus an HDD offered by its manufacturer as a 1 TB drive is reported by these OSes as a 931 GB HDD. Mac OS X 10.6 ("Snow Leopard"), uses powers of 1,000 when reporting HDD capacity.
In the case of "mega-", there is a nearly 5% difference between the powers of 1,000 definition and the powers of 1,024 definition. Furthermore, the difference is compounded by 2.4% with each incrementally larger prefix (gigabyte, terabyte, etc.). The discrepancy between the two conventions for measuring capacity was the subject of several class action suits against HDD manufacturers. The plaintiffs argued that the use of decimal measurements effectively misled consumers[53][54] while the defendants denied any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the law and that no class member sustained any damages or injuries.[55]
In December 1998, standards organizations addressed these dual definitions of the conventional prefixes by standardizing on unique binary prefixes and prefix symbols to denote multiples of 1,024, such as "mebibyte (MiB)", which exclusively denotes 220 or 1,048,576 bytes.[56] This standard has seen little adoption by the computer industry, and the conventionally prefixed forms of "byte" continue to denote slightly different values depending on context.[57][58]
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