Abstract: Improved disk pack media for data storage illustrated as comprising a pack of flexible magnetic recording disks perforated for partitioning and adapted for stacking each in a different respective rotational orientation to facilitate partitioning. All disks are hole-encoded in a common pattern, then stacked to dispose each in a unique rotational "misregistration" relative to all others -- thereby opening-up and/or closing-off adjacent "partition bores" and permitting associated automatic apparatus to selectively partition the pack and expose any desired disk-side for operation thereon.