IBM Direct Access Storage Product Manager, Alan Shugart, assigned the job to David L. Noble, who tried to develop a new-style tape for the purpose, but without success. Noble's team developed a read-only, 8-inch-diameter (200 mm) flexible diskette they called the "memory disk", holding 80 kilobytes of data. The original disk was bare, but dirt became a serious problem so they enclosed it in a plastic envelope lined with fabric that would remove dust particles. IBM introduced the diskette commercially in 1971.

The new device, developed under the code name Minnow, first shipped in 1971 as the 23FD, the program load component of the 2835 Storage Control Unit. and then as a standard part of most System 370 processing units and other IBM products. Internally IBM used another device, code named Mackerel, to write boot disks for distribution to the field.

Alan Shugart left IBM and moved to Memorex where his team shipped the Memorex 650 in 1972, the first commercially available read-write floppy disk drive. The 650 had a data capacity of 175 kB, with 50 tracks, 8 sectors per track, and 448 bytes per sector. The Memorex disk was "hard-sectored", that is, it contained 8 sector holes (plus one index hole) at the outer diameter (outside data track 00) to synchronize the beginning of each data sector and the beginning of a track.

More Info: en.wikipedia.org