A file system is the combination of software and hardware that supports storing information on a storage device. In the OS/2 operating system, the file system specifies how data is organized on the mass storage devices of the computer, such as hard disks and floppy disks.

Each drive is assigned a unique letter to distinguish it from other drives. A single hard disk can also be divided into two or more logical drives. A logical drive represents a portion of the hard disk and, like a physical drive, is assigned a unique letter to distinguish it from other physical and logical drives.

The file system organizes disks into volumes, directories, and files. A volume is the largest file system unit. It represents all the available storage on the logical drive. An optional volume name identifies the volume.

Volumes are subdivided into directories, which contain files and other subdirectories. Each volume has a root directory, which contains file and directory entries. All other subdirectories trace their ancestry back to the root directory. Each directory entry identifies the name, location, and size of a specific file or subdirectory on the disk. A file is one or more bytes of data stored on the disk. Subdirectories provide an additional level of organization and, like the root directory, can contain files and directory entries.

The file system also enables users and applications to access certain non-disk devices as if they were files. An example of such a device would be the printer, which can be accessed through the file system by using the printer's logical name, PRN, as a file name.