OS/2 allows more than one file system on a single storage device. If the device can have more than one partition (or volume), each partition can be initialized as an OS/2 partition and given a valid OS/2 file system. For each volume, OS/2 determines the type of file system the first time the volume is accessed by a function or when the medium in the drive changes. After that, OS/2 manages all input and output to that volume by using the corresponding dynamic link library.

OS/2 uses the volume label and serial number to ensure that the medium in the drive does not change while there are outstanding requests for input and output. Each volume has a volume label and a 32-bit volume serial number, stored in a reserved location in logical sector 0 at the time of formatting. If the volume label and serial number do not match, OS/2 signals the critical error handler to prompt the user to insert the volume that has the specified serial number and label. OS/2 maintains the connection between the medium and the volume label and serial number until all open files on the volume are closed and all search references and cache buffer references are removed. The system redetermines the type of file system and the volume label and serial number only when the medium changes.

OS/2 enables applications to:

• Determine and set the default drive using DosQueryCurrentDisk and DosSetDefaultDisk, respectively.

• Determine and set drive information using DosQueryFSInfo and DosSetFSInfo.

• Determine and set the write verification switch using DosQueryVerify and DosSetVerify. If the write verification switch is on, each time data is written to the disk, the data is verified to ensure it has been recorded correctly. These functions are provided for recording critical data.