What files can a floppy disk hold?

A floppy can hold any files that will fit into its very limited amount of space (by today's standards). A 3-1/2-inch Double Density (3.5" DD) disk holds only 720K of data while a 3-1/2-inch High Density (3.5" HD) disk holds double that at 1.44MB. (In actual numbers of bytes, it works out to 730,112 for the DD and 1,457,664 for the HD.) So, that could hold a fair number of MS Word documents and even more text files but would not hold many modern pictures and would most likely not hold even a single MP3.