Determine what filesystem a partition is of

Question

How does operating system know what filesystem a partition is using? In other words, how are FAT16/32, NTFS, ext2/3 etc. distinguished from each other?

Answer 1

First of all, the partition table has a byte in it that specifies the partition type. Secondly, every partition has different headers and structures, so with a bit of analysis it can be determined pretty much precisely.

Answer 2

About every filesystem has some header information which is called "superblock." Superblocks contain magic numbers or other info about the type of filesystem.

MBR partition table also stores a 8 bit value representing the partition type.

Answer 3

On linux when you mount a filesystem, you can pass -t ext3/ext3 etc - if you look in /etc/fstab (or equivalent) each drive probably has its fs type listed.

Then for automatically doing it, there is the superblock/equivalent (think windows types call it something else) ...

See this:

Superblock

Each file system is different and they have type like ext2, ext3 etc. Further each file system has size like 5 GB, 10 GB and status such as mount status. In short each file system has a superblock, which contains information about file system such as:

* File system type
* Size
* Status
* Information about other metadata structures

Taken from:

http://www.cyberciti.biz/tips/understanding-unixlinux-filesystem-superblock.html

Answer 4

Assuming you have an MBR then the details about the 4 primary partitions are found at 0x01BE. One of the sixteen bytes describing a partiton is a type identifier.

An id of 0x06 is fat16, 0x0B is FAT32, 0x07 is NTFS, 0x82 is a Linux partition.

Beyond that file-systems have structures at the specific locations within the partition that can be detected.

Answer 5

If you're using Win32 APIs on Windows, then you can call GetVolumeInformation (http://msdn.microsoft.com/en-us/library/aa364993.aspx) to determine the type of file system present on a given mounted volume.

For example, if you're trying to detect the file system present on D:, then you can call:

WCHAR FSType[512];    

if (GetVolumeInformationW(L"D:\\", NULL, 0, NULL, NULL, NULL, FSType, ARRAYSIZE(FSType))) {
    wprintf(L"FS type = %s\n", FSType);    
}

This will only work, however, if the file system is "recognized" and "mountable" by the running operating system.

Answer 6

There are several ways, depending on the hardware type.

Hard discs have a Master Boot Record followed by a Partition Table. The PT contains a list of the partitions on this drive. Each entry in that list contains (among other things) a numeric System ID field that specifies the partitions file system.

Floppy discs and most USB sticks do not have a PT. Here you have to look into the partition itself. The first partition sector (known as Boot Sector) usually contains a System ID in a completely different format from the System ID in the PT. Also, the location of the ID within the sector can differ between file systems.