The earliest floppy disks, invented at IBM, were 8 inches in diameter. They became commercially available in 1971
8-inch disk drive with diskette
In 1976 Shugart Associates introduced the first 5¼-inch FDD and associated media. By 1978 there were more than 10 manufacturers producing 5¼-inch FDDs, in competing physical disk formats: hard-sectored (90 KB) and soft-sectored (110 KB). The 5¼-inch formats quickly displaced the 8-inch for most applications, and the 5¼-inch hard-sectored disk format eventually disappeared
In 1984, IBM introduced the 1.2 megabyte dual sided floppy disk along with its AT model. Although often used as backup storage, the high density floppy was not often used by software manufacturers for interchangeability. In 1986, IBM began to use the 720 kB double density 3.5″ microfloppy disk on its Convertible laptop computer. It introduced the so-called “1.44 MB” high density version with the PS/2 line. These disk drives could be added to existing older model PCs.
Through the early 1990s a number of attempts were made by various companies to introduce newer floppy-like formats based on the now-universal 3½-inch physical format. Most of these systems provided the ability to read and write standard DD and HD disks, while at the same time introducing a much higher-capacity format as well. There were a number of times where it was felt that the existing floppy was just about to be replaced by one of these newer devices, but a variety of problems ensured this never took place. None of these ever reached the point where it could be assumed that every current PC would have one, and they have now largely been replaced by CD and DVD burners and USB flash drives.