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UNIX / Linux File Systems

All file systems perform the same basic functions, based on their fundamental goals: the intelligent organization of data and efficient control of and access to that data. As a result, most of them resemble each other to some extent, even if they are also different from each other in important ways. Even if two PC file systems differ greatly in terms of their internal architecture and structures, they can be made to resemble each other closely in their outward appearance. For example, Windows NT will support both FAT and NTFS partitions, which are totally different in terms of their internal structures, but have virtually the same interface for the user (and for software applications).

UNIX has been around for many decades, making it the oldest of all file systems used on PC hardware. UNIX file systems are also probably the most different from the other file systems used on PC, both internally and externally (referring to how the user accesses the file system). While most Windows users are accustomed to the Explorer-type interface for managing files and folders, UNIX files are usually managed with discrete text commands--similar to how DOS works (in fact, many principles of the FAT file system are based on UNIX.). There are graphical UNIX shells as well, of course, but many UNIX users (myself included) never use them.

The more important differences, however, are internal. UNIX file systems are designed not for easy use, but for robustness, security and flexibility. UNIX file systems offer the following features, and have for many years:

• Excellent expandability, and support for large storage devices.
• Directory-level and file-level security and access controls, including the ability to control which users or groups of users can read, write or execute a file.
• Very good performance and efficient operation.
• The ability to create "flexible" file systems containing many different devices, to combine devices and present them as a single file system, or to remotely mount other storage devices for local use.
• Facilities for effectively dealing with many users and programs in a multitasking environment, while requiring a minimum of administration.
• Ways to create special constructs such as logically linked files.
• Reliability and robustness features such as journaling and support for RAID.

If these features sound similar to those of NTFS, that's because UNIX and Windows NT/2000 now compete for much of the same market, so NTFS was given most of the capabilities that UNIX has. There are many other features as well, which differ from one implementation to another--there is no single "UNIX file system", any more than there is a single "UNIX operating system". Each UNIX variant (including the popular Linux for the PC, which itself has many different flavors) has a slightly different file system, though they are of course very similar to each other, and it is usually possible for different UNIX implementations to read each other's files.

UNIX file systems were one of the first (if not the first) to use the hierarchical directory structure, with a root directory and nested subdirectories. (Most of us are familiar with this from using it with the FAT file system, which works the same way). One of the key characteristics of UNIX file systems is that virtually everything is defined as being a file--regular text files are of course files, but so are executable programs, directories, and even hardware devices are mapped to file names. This provides tremendous flexibility to programmers and users, even if there is a bit of a learning curve at first.

Since few PC users run UNIX on their own machines, it's unlikely that you will ever actually use a UNIX file system directly. However, you may find yourself using a UNIX file system if you run a web site, for example, so understanding the basics of how UNIX works is a good idea. For more information, you may wish to consult this page, which provides a nice overview of the file system. This page provides more detail and also describes common UNIX file-manipulation commands. There are literally thousands of other sites and pages about UNIX on the Internet!

Next: BeOS File System (BFS)

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