When you access a floppy disk, you may receive one of the following error messages:
A:\ is not accessible.
The device is not ready.
Disk is not formatted
The disk in drive A is not formatted.
Do you want to format it now?
The same disk may work correctly with MS-DOS or Windows 95, or after you re-format the disk with Windows 98, Windows Millennium Edition, Windows NT, Windows 2000, Windows XP, or Windows Server 2003.
This problem occurs on disks that do not contain a media descriptor byte in the BIOS parameter block (BPB) of the boot sector. Some older preformatted floppy disks do not contain a media descriptor byte. Older product disks may also not have the media descriptor byte.
The media descriptor indicates the type of medium currently in a drive. With MS-DOS and Windows 95, you do not have to set the media descriptor byte. Therefore this problem does not occur with these older operating systems.
The media descriptor byte is located in the BPB of the boot sector at offset 21 (15h) and in the first byte of each FAT on the disk.
To resolve this problem, try some floppy disk recovery
softwares. They are usually very effective to recover data from such disks.