The IBM 3850 Mass Storage System was announced in October 1974. A combination of a new storage facility (right background) and IBM's widely used 3330-series disk subsystem (left background), the 3850 created the image of multiple magnetic disk devices -- similar to the way virtual storage used a computer's main memory as though it were much larger than it actually was. The storage facility serves as the system's "lending library," housing IBM data cartridges and transferring data from them to disk drives. The disk subsystem's 3830 Model 3 Storage Control created the image of many more disk units by continuously exchanging information with the storage facility and by using the same space on a disk pack to store different files at different times -- eliminating the need to dedicate that disk space to a single file. The 3850 system, shown here in engineering models, could be attached to IBM System/370 Models 145 through 168 running under Operating System/Virtual Storage 1 or 2.