fred langa traces in his articel the lineage of hard drives back to 1952: to ibm "nrz", "none-return-to-zero" encoding.

ramac, "random access method of accounting and control" was introduced by ibm september 13, 1956. the system used fifty metallic disks, each 1meter in diameter, tells gene franklin. the storage capacity was 5 megabytes. to reach that, they had to built a device in the size of a closet. when they turned it on, the whole box was shaking like a washing machine, franklin says. engineers at that time suggested the usage of a short wire. for saftey reasons. or - to put it in a historic folkloric way - to keep it from walking out the door.

the RAMAC had a servo system to move the actuator vertically and radially. the position were "detected" by detent marks on the actuators.The early comb actuators were hydraulic until IBM introduced the first voice coil motor in a drive in 1965 (Daniel Abramovitch and Gene Franklin, A brief history of disk drive control, IEEE Control Systems Magazine, June 2002)

storage space and price over the years.