per second. An access mechanism moves a pair of heads up and down to select a disk pair (one down surface and one up surface) and in and out to select a recording track of a surface pair. Several improved models were added in the 1950s. The IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month. The 350 was officially withdrawn in 1969. from the RAMAC program is generally considered to be the fundamental patent for disk drives. This first-ever disk drive was initially cancelled by the IBM Board of Directors because of its threat to the IBM punch card business but the IBM San Jose laboratory continued development until the project was approved by IBM's president. The 350's cabinet is long, high and wide. The RAMAC unit weighs about one ton, has to be moved around with forklifts, and was frequently transported via large cargo airplanes. According to Currie Munce, research vice president for Hitachi Global Storage Technologies (which acquired IBM's storage business), the storage capacity of the drive could have been increased beyond five million characters, 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. Nonetheless, double capacity versions of the 350 were announced in January 1959 and shipped later the same year. In 1984, the RAMAC 350 Disk File was designated an International Historic Landmark by The American Society of Mechanical Engineers. In 2002 at the Magnetic Disk Heritage Center a team led by Al Hoagland began restoration of an IBM 350 RAMAC in collaboration with Santa Clara University. In 2005, the RAMAC restoration project relocated to the Computer History Museum, Mountain View, California and is now demonstrated to the public in the museum's Revolution exhibition. IBM 353 The IBM 353, used on the IBM 7030, was similar to the IBM 1301, but with a faster transfer rate. It has a capacity of 2,097,152 (221) 64-bit words or 134,217,728 (227) bits and transferred 125,000 words per second. A prototype unit shipped in late 1960 was the first disk drive to use one head per surface flying on a layer of compressed air as in the older head design of the IBM 350 disk storage (RAMAC). Production 353s used self-flying heads essentially the same as those of the 1301. IBM 355 The IBM 355 was announced on September