File Systems Explained
Unix based operating systems use a file system based on a single root directory. This means Unix uses a virtual file system so the hierarchy does not have to exist on a specific hard drive or even on a local system. Add-ons to the file system, such as a USB drive have to be "mounted" in order to be accessed by the file system. Mounting is necessary because unlike in Windows (NTFS) there are no extra drives (C:, D:, E:, etc.) to add the device to, instead /mnt is needed. Add-onss can be named (as in hda1) but this is for reference purposes, not organizational ones. ext2 (second extended file system) was created for Linux operating systems. ext is not a journaling file system, though ext3 is.
ext3, or the third extended filesystem, is popular with current Linux operating systems. It allows journalling which records changes which happen to a journal. This happens before the change are writen. Though this hurts performance it increases reliability and data protection. Because changes are recorded recovery can occur simply by rolling back changes and returning to a configuration which was correct. Journalling can be done by different methods which offer different levels of security. ext3 is highly compatible with ext2, though journalling and a few other things are not supported.
ReiserFS is a file system which is supported by Linux after the 2.4.1 kernal, though it unique from ext3. This was first journaling file system to be included in the Linux kernel. Distributions like SuSE, Xandros, Slackware, and Linspire use this as their default file system. Its most hyped feature is metadata-only journaling, but is also supports functions like online resizing and tail packing (in order to minimize fragmentation). ReiserFS is known for its efficiency and speed, especially when dealing with small files. The newest version of this is Reiser4.
All the examples above are disk file systems. Though these are the most commonly referred to, others do exist. A network file system enables a computer to reach files over a network as it would data on local disks. Examples of network files systems include Sun's NFS, Distributed File System, and AppleShare.
Anything which is not a network or disk file system is usually as a "specialty" file system. These are usually built for proprietary systems and are not really something which will ever come up in day to day work. It should be known that they exist, but past that they are generally a non-factor.