High Quality Content by WIKIPEDIA articles! The IBM 305 RAMAC, publicly announced on September 13, 1956, was the first commercial computer that used a moving head hard disk drive (magnetic disk storage) for secondary storage. RAMAC stood for "Random Access Method of Accounting and Control". Its design was motivated by the need for real-time accounting in business. The first RAMAC to be used in the US auto industry was installed at Chrysler`s MOPAR Division in 1957. It replaced a huge tub file which was part of MOPAR`s parts inventory control and order processing system. The 305 was one of the last vacuum tube computers that IBM built. The IBM 350 disk system stored 5 million 8-bit (7 data bits plus 1 parity bit) characters. It had fifty 24-inch-diameter (610 mm) disks. Two independent access arms moved up and down to select a disk, and in and out to select a recording track, all under servo control. Average time to locate a single record was 600 milliseconds. Several improved models were added in the 1950s. The IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month in 1957 dollars, equivalent to a purchase price of about $160,000. More than 1,000 systems were built. Production ended in 1961; the RAMAC computer became obsolete in 1962 when the IBM 1405 Disk Storage Unit for the IBM 1401 was introduced, and the 305 was withdrawn in 1969.