designed for use with the IBM 7000 series mainframe computers and the IBM 1410. The 1301 stores 28 million characters (168,000,000 bits) per module (25 million characters with the 1410). Each module has 25 large disks and 40 user recording surfaces, with 250 tracks per surface. The 1301 Model 1 has one module, the Model 2 has two modules, stacked vertically. The disks spin at 1800 rpm. Data is transferred at 90,000 characters per second. A major advance over the IBM 350 and IBM 1405 is the use of a separate arm and head for each recording surface, with all the arms moving in and out together like a big comb. This eliminates the time needed for the arm to pull the head out of one disk and move up or down to a new disk. Seeking the desired track is also faster since, with the new design, the head will usually be somewhere in the middle of the disk, not starting on the outer edge. Maximum access time is reduced to 180 milliseconds. The 1301 is the first disk drive to use heads that are aerodynamically designed to fly over the surface of the disk on a thin layer of air. This allows them to be much closer to the recording surface, which greatly improves performance. The 1301 connects to the computer via the IBM 7631 File Control. Different models of the 7631 allow the 1301 to be used with a 1410 or 7000 series computer, or shared between two such computers. The IBM 1301 Model 1 leased for $2,100 per month or could be purchased for $115,500. Prices for the Model 2 were $3,500 per month or $185,000 to purchase. The IBM 7631 controller cost an additional $1,185 per month or $56,000 to purchase. All models were withdrawn in 1970. IBM 1302 The IBM 1302 Disk Storage Unit was introduced in September 1963. Improved recording quadrupled its capacity over that of the 1301, to 117 million 6-bit characters per module. Average access time is 165 ms and data can be transferred at 180 K characters/second, more than double the speed of the 1301. There are two access mechanisms per module, one for the inner 250 cylinders and the other for the outer 250 cylinders. As with the 1301, there is a Model 2 which doubles the capacity by stacking two modules. The IBM 1302 Model 1 leased for