The OS/2 FAT file system recognizes file objects created by the DOS FAT file system. This means that applications running under the OS/2 operating system (these include both OS/2 applications and DOS applications running in a DOS Session) can access file objects created by applications running under DOS.

Because the OS/2 FAT file system supports the same directory structure as the DOS FAT file system, applications running under DOS can access files and directories created by the OS/2 FAT file system.

However, the High Performance File System (HPFS) does not support the same directory structure as the DOS FAT file system. Therefore, the DOS FAT file system will not recognize file objects created by HPFS. This means that if you start the computer with DOS, applications running under DOS cannot access files and directories on HPFS disks.

DOS applications running in a DOS Session under the OS/2 operating system can recognize files and directories on both FAT and HPFS disks. A request from a DOS Session to read a file on a FAT disk is handled by the OS/2 FAT file system. Similarly, a request from a DOS Session to read a file on an HPFS disk is handled by the OS/2 High Performance File System.