File size

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File size measures the size of a computer file. Typically it is measured in bytes with a prefix. The actual amount of disk space consumed by the file depends on the file system.

The maximum file size a file system supports depends on the number of bits reserved to store size information and the total size of the file system. For example, with FAT32, the size of one file cannot be equal or larger than 4 GiB.

Some common file size units are:

1 KiB = 1,024 bytes

1 MiB = 1,048,576 bytes ^[1]

1 GiB = 1,073,741,824 bytes ^[2]

1 TiB = 1,099,511,627,776 bytes ^[3].

These units are often described using the terms KB, MB, GB and TB respectively. This is technically imprecise, because the prefixes kilo, mega, giga and tera refer respectively to multiplication by 10^3, 10^6, 10^9 and 10^12. However, the power-of-two based prefixes have yet to find widespread usage, so some ambiguity remains. For example, a hard disk which is described by its maker as having a capacity of 200 GB will have a capacity very close to 200 * 10^9 bytes. Yet, when such a disk is freshly formatted and installed in a machine running Microsoft Windows XP, the operating system will report the size as approximately 186 GB. This value can vary slightly depending on the exact capacity of the drive, which file system is used and so on. This is because Windows is actually reporting the size in GiB and 186 GiB is approximately equal to 200 GB.