On September 4, 1956 IBM announced the IBM 350 disk storage unit or 350 RAMAC for the IBM 305 RAMAC, which they introduced on September 13, 1956. The IBM 305 RAMAC was the first commercial computer that used a moving head hard disk drive (magnetic disk storage) for secondary storage. One day later, on September 14, 1956, IBM announced the 650 RAMAC system, which paired an IBM 650 computer with the IBM 355 RAMAC disk storage unit. However, the 650 RAMAC was a modification of the best-selling IBM 650 system rather than a new system designed specifically to use the RAMAC hard drives.
"The 305 was one of the last vacuum tube computers that IBM built. It weighed over a ton. The IBM 350 disk system stored 5 million 7-bit (6 data bits plus 1 parity bit) alphanumeric characters (5 MB). 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computer became obsolete in 1962 when the IBM 1405 Disk Storage Unit for the IBM 1401 was introduced, and the 305 was withdrawn in 1969.
"Programming the 305 involved not only writing machine language instructions to be stored on the drum memory, but also almost every unit in the system (including the computer itself) could be programmed by inserting wire jumpers into a plugboard control panel. . . .
"Currie Munce, research vice president for Hitachi Global Storage Technologies (which has acquired IBM's hard disk drive business), stated in a Wall Street Journal interview that the RAMAC unit weighed over a ton, had to be moved around with forklifts, and was delivered via large cargo airplanes. According to Munce, the storage capacity of the drive could have been increased beyond five megabytes, but IBM's marketing department at that time was against a larger capacity drive, because they didn't know how to sell a product with more storage" (Wikipedia article on IBM 305 RAMAC, accessed 10-22-2013).