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1898 - Magnetic Recording Patent

1956 - IBM Type 305 RAMAC - 5 MB magnetic disk memory. Housing unit size of 2 washing machines. 50 disks, each 24 inches in diameter.

1962 - Removable disk drive. Industry plans on making lots of money selling replaceable disk packs. Cost of tape keeps numbers low. Customers leap at any other technology that is better.

1970 - IBM builds first floppy disk drive (8 inch, 360 rpm) using flexible plastic diskettes encased in a square jacket containing a surface wiper. Indexed with a photocell used to detect a hole in the disk. 32 Hard sectors. The head was raised from the surface of the disk for each track change and a track change required an unload operation, a stepping operation, a loading operation (settling) resulting in very long seek times.

1973 - IBM Winchester (hard) Drive -- has two 30 million character spindles, hence name of 30-30 and ultimate name of Winchester (From the rifle). Uses air bearing for heads.

Control Data (CDC) and others develope the Storage Module Device (SMD) interface (computer independent). Establishes a simple interface to hard drives that can be built by any vendor. This idea catches on and subsequent interfaces (ATA, SCSI, MFM, RLL, IDE) are established as industry standards.

IBM 3470 diskettes were single-side, single density and used 77 tracks, each with 26 sectors of 128 bytes. The recording technique was FM and a magnetic transition within a recorded cell was a one while no transistion was read as a zero. (Assume zero until find one.)

Floppies have been made in diameters of 14", 10", 9", 8" (CPM PC's), 5.25", 3.5", 2.5", and 2".  Of those, only 8", 5.25", and 3.5" diameter disks are widely used.