IBM 3850

The IBM 3850 Mass Storage System[1] (MSS) was an online tape library used to hold large amounts of infrequently accessed data.

[3] Starting in the late-1960s IBM's lab in Boulder, Colorado began development of a low-cost mass storage system based on magnetic tape cartridges.

These cartridges were held in a hexagonal array of bins in the IBM 3851 Mass Storage Facility.

Cartridges were moved into and out of read stations by two motorized accessor arms, electrically connected via flat cable on a drum.

When free disk space was required a group of cylinders were selected to be destaged to tape, these were transferred with minimal or no change of format.