Extended density format
The extended density format, or XDF, is a type of formatting for high density 3.5" and 5¼" floppy disks that allows for increased data storage. Using XDF, a 3.5" disk can store 1860 kilobytes of data and a 5¼" disk, 1540 kilobytes.
XDF is natively supported by PC DOS versions 7 and 2000, as well as OS/2 Warp 3 and higher. Floppy disks using XDF can only be read in floppy disk drives directly connected to a computer using a floppy disk controller. This condition means USB floppy disk drives are not capable of reading an XDF disk. The first cylinder of an XDF disk uses normal FAT12 formatting, allowing for the drives and operating systems that do not support XDF to be able to read that part of the disk. This first cylinder can be used to store a readme file or XDF drivers.