The Control Data Corporation (CDC) 9877 was a removable hard disk pack, introduced in 1974 for use in the CDC 9762 disk drive. The drives were standalone devices, connected to mini-computers from the likes of DEC or Data General via an interface known as Storage Module Device (SMD).
Of the five 14-inch platters, three contained data and head carriage positioning information, and two were for data protection. The CDC 9877 could store 80 MB.
Unlike modern hard disks which contain sealed magnetic platters, the CDC 9877 and similar disk packs contained removable sets of platters inside a protective canister with a lifting handle which was turned to release the cover once the pack was in the drive.