Many developments, devices, and methods were transient, although filling a need whenever current. Although the development of the floppy disk, another IBM invention, opened up the personal computer market. It has been replaced by memory sticks or memory cards. Since it was originally developed for the input of large computers, it was an inherently unsafe as a storage medium since the reading and recording heads in contact with the recording surface. This limited both the capacity and speed of operation. The optical disk has less use since high-speed broadband has allowed software to be downloaded at an acceptable rate, thus reducing the need distribution of software on compact disk.
The only reliable random access device available in those early years was the magnetic drum is rotated on the vertical axis with reading and writing heads mounted against its surface. It's most notable use is probably the post office/ BT subscriber trunk dialling.
IBM must also be credited the development of modern hard disk systems. Before IBM developed the Winchester disk disk, surfaces had to be ground and balanced on their axes so that the reading and recording heads could be aligned close to the surface. Any inbalance caused destruction of the recording surface. The Winchester disk principle allowed the heads to rest on the surface of the disc and effectively fly over the surface of the disc as it got up to speed. Mechanisms mechanisms for controlling movement of the head accurately began to be both more accurate and much lighter. The whole disk and mechanism were sealed in a robust container in an inert gas.
As the reliability accuracy of servo systems developed and the number of recording tracks increased, reliability increased accordingly and the whole disk mechanism got lighter and more manoeuvrable. Storage of terabytes of data on a three and half inch disc is quite phenomenal