At IBM in 1952, Arthur J. Critchlow began the Source Recording project at the new IBM research lab in San Jose, California, under the direction of Reynold B. Johnson. The purpose was to find a better method than punched cards or drums or tape to store and access information. They read an article by Jacob Rabinow at the National Bureau of Standards in the August 1952 issue of Electrical Engineering about "The Notched-Disk Memory" that stored magnetic pulses on thin metal disks mounted vertically in a doughnut-shaped ring. Each disk had a notch to align magnetic read/write heads. Critchlow adopted this magnetic disk idea in February 1953 and Johnson began work at San Jose on a 50-disk system with the capacity of 50,000 punched cards, or 4 million characters. In April 1953, William A. Goddard headed a team of 4 engineers to develop the disk device. In May, he adopted the "air head" method of maintaining a uniform head-surface gap of .002 inch using a forced air cushion. In June a successful test was completed with the air head reading a writing digital data on the surface of a 16-inch aluminum disk sprayed with iron oxide paint. By October, spray paint was replaced by spin coating, and a servo-controlled cable-and-pulley carriage was used to successfully locate random tracks on the spinning disk. In February 1954, data was being transferred to and from a card reader. During 1954 a Model II was designed and built with a 50-disk array mounted on a vertical shaft. This model was given its first public demonstration in May 1955 as the Random Access Memory Accounting Machine, or RAMAC. An improved Model II was demonstrated at the February 1956 Western Joint Computer Conference. Each disk was 24 inches in diameter and 0.1 inch thick and separated from other disks by 0.3 inch spacers. The disks revolved at 1200 rpm and were accessed by a single read/write head that moved up and down the stack of platters Each disk had 100 circular tracks with a density of 500 characters per track, recorded by IBM's NRZI variable density method of 100 bits per inch on the inner track and 55 bits per inch on the outer track. This was the equivalent of storing 5 MB on a magnetic drum 13 inches diameter and 42 feet long. The disk array became the IBM 350 Disk Storage, and deliveries to customers began in June 1956 for a monthly lease of $750. The IBM 1301 Disk Storage was announced June 2, 1961. Each module had 25 disks and could store 28 MB. Up to 10 modules could be added to a computer for a maximum of 280 MB. Each disk had 50 tracks per inch with 520 bits per inch density, rotating at 1800 rpm. This was first used in the SABRE airline reservation system in 1961 that used 6 magnetic drums and 16 modules of the 1301 Disk Storage unit. The drums only had capacity for 1.1 MB each, but were 20 times faster in access time. In September 1963, the 1302 Disk Storage increased capacity 4 times by doubling the tracks per inch and the bits per track. The 1316 Disk Pack announced October 11, 1962, (at first called the 1311 Disk Storage Drive) was a removable pack of 6 disks, with a capacity of 2 MB, and popular with smaller computers and a versatile storage medium.
Magnetic Disk Heritage Center in San Jose and the RAMAC anniversary
