January 6, 1975. Master drive on IBM 1620 or IBM 1710 system and can control up to three Model 2 drives. Does not support any special features. Introduced October 11, 1962. Withdrawn May 12, 1971. Master drive on an IBM 1401 system and can control up to four Model 2 drives. Introduced October 11, 1962. Withdrawn February 8, 1971. Master drive on an IBM 1410, IBM 7010, or IBM 7740 system and can control up to four Model 2 drives. Direct Seek comes as standard on this model. Introduced January 7, 1963. Withdrawn May 12, 1971. No information available, probably a master drive. Introduced March 5, 1968. Withdrawn February 2, 1971. No information available, probably a slave drive to Model 6. Introduced March 5, 1968. Withdrawn February 2, 1971. The optional special features are: Direct Seek: Without this option every seek returns to track zero first. Scan Disk: Automatic rapid search for identifier or condition. Seek Overlap: Allows a seek to overlap a single read or write, and any number of other seeks, when multiple drives are in use. Track Record: Increases the capacity of the disk by writing a single large record per track instead of using 20 separate sectors. A track can hold 2,980 characters in 6-bit 'Move Mode", and 2,682 7-bit characters in "Load Mode", giving the drive a total capacity of 17,880,000 bits in 6-bit mode, and 18,774,000 bits in 7-bit mode. The master drives, Models 1, 3, 4, and 5, which contain extra power supplies and the control logic, are about a foot wider than the Model 2 slave drive. IBM System/360 and other IBM mainframe HDDs IBM 2302 The IBM 2302 is the System/360 version of the 1302, with track formatting in accordance with S/360 DASD architecture rather than 7000 series architecture. It uses a non-removable module of 25 platters, of which 46 surfaces are used for recording. The 2302 Model 3 contains one module and the Model 4 two. There are two independent access mechanisms per module, one for the innermost 250 cylinders, and one for the outermost 250, tracks available to each access mechanism are called an access group. The access mechanism provides one read/write head per track. Average rotational delay is 17 milliseconds (msec), and maximum is 34 msec. Maximum seek time per access group is 180 msec. The track size is 4985 bytes; with formatting information and alternate tracks, module