The IBM 3350 Direct Access Storage Facility, was code-named Madrid,(not sure why) was introduced in 1975 for use with IBM System/370.
It was the dominant product in the industry for its time . It had non-removable disk packs that were sealed. The disk geometry was 555 cylinders, 30 heads, with 19K bytes per track which gave the it a storage capacity of 317,498,850 bytes. Each unit had contained two HDAs and they were installed in “strings” of units. How far we have come.less