There were two floppy disk technologies used in PCs. The 5.25" was superseded by the 3.5" diskettes in the mid-1990s.5.25" Square Flexible EnvelopeThe first floppy was a low-density 360KB 5.25" diskette. After the 1.2MB drive came out in 1984, 360KB diskettes were still used to distribute software, because the 1.2MB drive supported the earlier media.3.5" Rigid Plastic CaseThe 720KB 3.5" floppy was introduced on IBM's Convertible laptop. Capacity doubled to 1.44MB with the PS/2 line, and 1.44MB drives supported 720KB media. The visible difference between the two was that the 1.44MB diskette had a hole in the upper left corner. IBM offered an extra-high density 2.88MB drive on selected PCs that was 1.44MB compatible, but the format never caught on.Floppy Disk Formats 720KB 3.5" DS/DD 1.44MB 3.5" DS/HD 2.88MB 3.5" DS/ED (IBM only) 360KB 5.25" DS/DD 1.2MB 5.25" DS/HD DS = double sided DD = double density HD = high density ED = extra=high density.