History of IBM magnetic disk drives#Early IBM HDDs

The IBM 350 was the world's first hard drive and 305 RAMAC was introduced to the public on September 4, 1956 as part of the computer IBM. RAMAC stands for Random Access Method of Accounting and Control.

The development of the drive began in the early 1950s in a new research center of IBM in San Jose (California ), led by Reynold B. Johnson. Punch cards were until then the art and business base of IBM. The users they had to rearrange and to interpret often on tables in each case to meet the task. After IBM was looking for alternatives only when the keenest competitor bought out the technically leading manufacturer of drum memory and the UNIVAC magnetic tape. The new team of IBM sought a solution that combined short access time with great capacity. The decision to implement the idea of a disk fell in April 1953.

An IBM 350 is 1.73 m high, 1.52 m wide, 74 cm deep, and can hold approximately 5 MB of data. Containing 50 aluminum plates of 61 cm in diameter, which are coated on both sides and is stacked on a magnetizable shaft at intervals of 8 mm. The plate stack is rotated at 1200 revolutions per minute. To store and read data two arms are driven with write and read heads vertically to the respective plates and then lower or higher than this. The heads are held by compressed air at a distance from the plates. A corresponding compressor is included in the IBM 350. The access time is on average 0.6 seconds.

IBM 350 were not sold but leased for $ 650 per month. On August 18, 1969 have all been taken off the market.