Drum

Drums were the predecessor magnetic storage technology to disks; they were (as the name suggests) in physical form a drum, and generally had a head per track (like fixed-head disks.

The very first drums were actuallly used for main memory on some very early computers; and also on slightly later, but low-end, ones. Once core memory appeared, drums were only seen in the role of high-speed secondary storage; often being used for swapping or paging purposes.

Drums likely fell out of use because they took more physical space than a disk with the equivalent surface area. A number of disk platters, given in total a significantly greater amount of storage, could be stacked in the volume occupied by a single drum.