The Directories->Compare menu item activates a Compare Directories dialog that can compare the current files in the two file windows. Comparisons may be based on either a match in the file name, size and/or date/time, a difference in file names or a binary difference between files of the same name.
File name comparison on FAT drives is based on the longname EA if one exists, making comparisons between FAT and HPFS file system directories possible.
Accelerator Keys - Ctrl Shift ?