Improved flexible disk pack magnetic storage systems and associated elements are illustrated as adapted for end-wise pneumatic partitioning and indicate, among other features, the use of «rim means» in the gap between adjacent flexible disks and surrounding holes therein, to better isolate the axial pressurized air streams through such holes from «non-selected» gaps and also to provide a reference surface for registration of the disks in the course of compressing the stack together; this «rim means» including «annulets» surrounding the holes not communicating pneumatically with a given gap and «semi-annulets» partly surrounding other holes which are in pneumatic communication with the gap -- and wherein such holes are circular except for the «in-communication» holes or orifices which are preferably enlarged by a «crescentic cut-out» opposite the respective «semi-annulet»