IBM announced the world’s first HDD, the 3.75MB RAMAC 350 disk storage unit, 69 years ago today — unit weighed more than a ton, 50 platters ran at 1,200 RPM from Latest from Tom's Hardware on 2025-09-14 13:15 (#70168) On this day in 1956, IBM announced the RAMAC 350 Disk Storage Unit, packing an awe-inspiring 3.75MB of data across 50 magnetic platters, each spanning 24-inches in diameter and spinning at 1,200 RPM.