Hard disk drive

The first hard drive was build by Jacob Rabinow, who was a researcher for the predecessor of the National Institute of Standards and Technology (NIST). Rabinow was an expert in magnets and mechanical engineering, and he'd been asked to build a machine to do magnetic storage on flat sheets of media, almost like pages in a book. He decided that idea was too complex and inefficient, so, stealing the idea of a spinning disk from record players, he built an array of spinning magnetic disks that coul be read by a single head. To make that work, he cut a pizza slice-style notch out of each disk that the head could move through to reach the approriate platter. Rabinow described this as being "like reading a book without opening it."

The first commercially available hard disk appeared 7 years later in 1956, when IBM introduced the 350 disk storage unit, as part of the 305 RAMAC computer system.
—Andy Warfield (July 27, 2023) "Building and operating a pretty big storage system called S3" All Things Distributed