File size is a measure of how much data a computer file contains or, alternately, how much storage it consumes. Typically, file size is expressed in units of measurement based on the byte. By convention, file size units use either a binary prefix (as in megabyte and gigabyte) or a metric prefix (as in mebibyte and gibibyte).
When a file is written to a file system, it may consume slightly more disk space than the file requires. This is because the file system rounds the size up to include any unused space left over in the last disk sector used by the file. A sector is the smallest amount of space addressable by the file system. The size of a disk sectors is several hundred or several thousands bytes. Although smaller sector sizes allow for denser use of disk space, they decrease the operational efficiency of the file system.
The maximum file size a file system supports depends not only on the capacity of the file system, but also on the number of bits reserved for the storage of file size information. The maximum file size in the FAT32 file system, for example, is 4,294,967,295 bytes, which is one byte less than four gigabytes.
|Traditional units||Decimal for comparison|
|Name||Symbol||Binary||Number of bytes||Equal to||Name||IEC||Decimal||Number of bits||Equal to|
|Kilobyte||KB||210||1,024||1024 B||Kilobit||kbit||103||1,000||1000 bit|
|Megabyte||MB||220||1,048,576||1024 KB||Megabit||Mbit||106||1,000,000||1000 kbit|
|Gigabyte||GB||230||1,073,741,824||1024 MB||Gigabit||Gbit||109||1,000,000,000||1000 Mbit|
|Terabyte||TB||240||1,099,511,627,776||1024 GB||Terabit||Tbit||1012||1,000,000,000,000||1000 Gbit|
|Petabyte||PB||250||1,125,899,906,842,624||1024 TB||Petabit||Pbit||1015||1,000,000,000,000,000||1000 Tbit|
|Exabyte||EB||260||1,152,921,504,606,846,976||1024 PB||Exabit||Ebit||1018||1,000,000,000,000,000,000||1000 Pbit|
|Zettabyte||ZB||270||1,180,591,620,717,411,303,424||1024 EB||Zettabit||Zbit||1021||1,000,000,000,000,000,000,000||1000 Ebit|
|Yottabyte||YB||280||1,208,925,819,614,629,174,706,176||1024 ZB||Yottabit||Ybit||1024||1,000,000,000,000,000,000,000,000||1000 Zbit|
- JEDEC Solid State Technology Association (December 2002). "Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits" (PDF). JESD 100B.01. p. 8. Retrieved 2009-04-05.
- "Microsoft Extensible Firmware Initiative FAT32 File System Specification, FAT: General Overview of On-Disk Format". Microsoft. 2000-12-06. Retrieved 2011-07-03.