Why is that when I format my pen drive with a FAT32 file system, I get more space to work with?

Question

Possible Duplicate: Why is the effective hard drive size lower than the actual size?

I have a 16 GB pen drive. When I formatted it with FAT32, I got 14.8 GB to work with...while using NTFS I got 14.7 GB. Where did the 100 MB go?

Answer 1

Filesystems store meta information (information about the files). FAT follows a legacy structure which was designed for small disks and low memory. Modern filesystems can have many additional features, backups of strucutres, and more information about the files themselves (permissions for example).

Cluster size (block size) is also a factor. This is the size of units which can be associated to a file. If it is 4k for example, then an average 2k per file is lost, because the FAT will not have the resolution to deal with details smaller than that. NTFS's default cluster size can be smaller than FAT32's, giving you a larger database about these allocation units which costs more space against the device's unallocated size.

A number of structures are allocated by default so it is understandable that there is a difference. If you start filling the drive with files the difference can grow even bigger - or NTFS can make up for this space originally lost, depending on the style you use the file system (few large files / many small ones).

Answer 2

The reason for this is that every filesystem needs a specific amount of memory (storage) to build the filesystem structure (list and position on the block device of directories, files, ... called ToC (Table of Contents), metadata, filesystem superblock, ...) on the storage device.

So you see FAT32 just needs 100 MB less than NTFS.

See File system for more information.