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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).[1]

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.[2]

Conversion table
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 [3] PB 250 1,125,899,906,842,624 1024 TB Petabit Pbit 1015 1,000,000,000,000,000 1000 Tbit
Exabyte [4] EB 260 1,152,921,504,606,846,976 1024 PB Exabit Ebit 1018 1,000,000,000,000,000,000 1000 Pbit
Zettabyte[citation needed] 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[citation needed] 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

See alsoEdit


  1. ^ 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. 
  2. ^ "Microsoft Extensible Firmware Initiative FAT32 File System Specification, FAT: General Overview of On-Disk Format". Microsoft. 2000-12-06. Retrieved 2011-07-03. 
  3. ^ "the definition of petabyte". Retrieved 2017-07-02. 
  4. ^ "the definition of exabyte". Retrieved 2017-07-02.