XDF is eXtended Density Format diskette, a format by IBM similar to Microsoft DMF.

These are 3.5" HD diskettes with special format, so that they reach 1840 Kb instead of 1440 Kb.

IBM used it to distribute disk images of some OS like PC DOS 7. These images have extension XDF.

Program XDF.COM is a TSR to read/write XDF diskettes.

Program XDFCOPY.EXE is the XCOPY version for XDF diskettes. It should manage XDF images too.