This is an old hard disk, 31 inches in diameter. The disks were built by Data Products Corp and were originally used on SDS 940 computers (Scientific Data Systems - long since defunct).

SDS 940s originally cost one million dollars (around 1968).

The entire drive assembly was over 6 feet tall, with a stainless steel shaft that went up the center. There were a total of 32 disks (platters) on the shaft.

Both sides of each disk were writable, with a total storage of 68 MB for the entire drive (all 32 disks). So that means this disk held roughly 1 MB on each side.

The white lines are where a solution was applied after the disk was removed from the drive assembly. The solution caused the data clusters to be visible.