History (1961): Flying Heads Improve HDD Capacity and Speed

This article comes from the Computer History Museum.

1961: Flying heads improve HDD capacity & speed
Commercial success of the “slider” in the IBM 1301 established a model for the industry

IBM 1301 disk storage unit

(Courtesy International Business Machines Corporation)

IBM, San Jose, CA began an Advanced Disk File (ADF) project to achieve 10x the storage capacity with 1/10 the access time of the Model 350 RAMAC unit in 1957. Announced in 1961 and first shipped to customers in 1962, the Model 1301 Disk Storage Unit met these goals using a dedicated arm with an aerodynamically-contoured electromagnetic R/W head.

Called a slider, the head ‘flew’ above the surface of each disk on a layer of moving air that formed a hydrodynamic bearing. Based on a concept described by IBM engineer Jake Hagopian in 1954, the Model 353 drive designed for the 7030 (Stretch) system and a competing unit from Bryant Computer Products shipped with flying heads before the 1301, but it was the commercial success of the latter product that established the combination of a flying head with one head per disk surface as a standard for virtually all future HDD system generations.

In 2000, Al Shugart listed the flying head as one of the four most significant technical developments in storage history.

Developed under program manager Shugart, the 1301 team included Bill Gross, Ken Haughton and Russ Brunner and led by Jack Harker.

A 1301 module comprised twenty five 24-inch disks spinning at 1,800rpm that stored a total of 28 million characters.

Multiple sliders mounted on a comb-like arm structure presented a separate head to each disk surface to improve data access speed by eliminating the delay incurred in moving a head from one disk to another. By eliminating the external pressurized air supply of the 350, the average head-to-surface distance decreased from 800 down to 250 microinches and storage capacity (areal density) increased to 26,000 bits per square inch, 13 times the RAMAC number.

The SABRE airline reservation system pioneered by American Airlines and IBM in the 1960s employed sixteen 1301 units.