Storage Devices and File Systems

OS/2 file systems store information on mass storage devices. These devices are usually hard disks or floppy diskettes, but can be other media, such as CD-ROM.

Each drive (or device) is assigned a unique letter to distinguish it from other drives. On most personal computers, drive A is the first floppy disk drive, drive B is the second floppy disk drive, drive C is the first hard disk drive, and drive D is the second hard disk drive.

A single hard disk can be divided into two or more partitions, each of which are then viewed as a separate logical drive. A logical drive, like a physical drive, is assigned a unique letter to distinguish it from other physical and logical drives. FDISK is the OS/2 utility used to partition physical storage devices.

A personal computer running the OS/2 operating system can have up to 26 logical disk drives.

Each logical storage device can be managed by a different file system. The file system attached to a storage device manages that device. A user attaches a file system to a storage device by:

Loading the file system driver during system initialization (by including an IFS= statement in CONFIG.SYS).
Formatting the storage device by using the format options for the file system.

During installation of the OS/2 operating system, users have the option of formatting hard disks with the FAT file system or with the (HPFS). If the user chooses to use the HPFS, an IFS= statement is added to the CONFIG.SYS file so that HPFS is loaded automatically during each system startup. During formatting, the file system driver is associated with the logical storage device or drive letter of the hard disk.

When an application calls a file system function, the operating system directs the request to:

The installable file system managing the storage device, or
The file system used to format the storage media manages that media each time the system is started, as long as the file system is loaded during system start-up. The operating system directs file system requests for a storage media to the file system that formatted the media. If no file system recognizes the format of the media, the OS/2 FAT file system attempts to manage that media. This might occur when the file system used to format the storage media is not loaded during system startup (the IFS= statement was removed from the CONFIG.SYS file after OS/2 installation). If the OS/2 FAT file system cannot recognize the media format (the media might have a different directory structure), the user receives an error when attempting to access the media.
For example, assume a system is configured with diskette drive A and hard disk drives C and D. During OS/2 installation, the user elects to format drive C using HPFS. Drive C is, then, managed by HPFS. Drive D was formatted with the FAT file system, so it is managed by the OS/2 FAT file system, as is diskette drive A (removable media cannot be formatted using HPFS). When an application calls DosOpen to open a file on drive C, the operating system directs the request to HPFS. When an application calls DosOpen to open a file on drive A, the operating system directs the request to the OS/2 FAT file system.
If HPFS is not loaded during system startup, the FAT file system will receive file system requests made for drive C. However, because HPFS supports a different directory structure than the FAT file system does, the OS/2 FAT file system cannot recognize file objects on the disk. The user will receive an error when attempting to gain access to the disk.
Users can determine which file system was used to format a storage device by using the CHKDSK utility. CHKDSK displays a message indicating which file system manages the specified drive. Because DOS does not use extended attributes, a user must use CHKDSK in an OS/2 session rather than in a Dos Session to examine a FAT partition.
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