<P> 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). </P> <P> When a file is written to a file system, which is the case in most modern devices, 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 .) The wasted space is called slack space or internal fragmentation . Although smaller sector sizes allow for denser use of disk space, they decrease the operational efficiency of the file system . </P>

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