Since all removable media do not have a serial number or have duplicate serial number (bulk formatted floppies), Windows 95 can not safely perform any volume tracking based on the volume serial number. To get around this problem, an FSD would always assign a unique serial number to a removable media on the very first MOUNT call to the media. (This operation is not necessary if the FSD generated unique number has already been written to this media). This number now identifies each media for volume tracking.