A pass-thru cassette magazine performs several functions beyond vertically holding a plurality of data cassettes in a position randomly accessible to a data storage subsystem picker assembly, including locking the data cassettes within corresponding storage cells in either an import or export position when the magazine is not interfaced to the storage subsystem (that is during handling by an operator). The "locked" position indicates that a data cassette cannot be removed from the magazine without a force of approximately one kilogram or greater. When a magazine is interfaced to the storage subsystem, the magazine is interlocked thereto such that the magazine cannot be removed without releasing the interlock. While the magazine is interlocked, the lock on the data cassettes is disabled so that the data cassettes can be freely picked by the picker assembly or removed or inserted by an operator. If a data cassette is in a position other than import or export, a potential problem exists and the interlock mechanism release is disabled thus requiring all data cassettes to be properly positioned before the magazine could be removed from the storage subsystem.