The first hard drive was as big as two refrigerators and held under four megabytes
IBM's first production hard disk, the 350, shipped in 1957 as part of the 305 RAMAC computer. Roughly the size of two large fridges, it spun a stack of 52 platters to hold five million characters, about 3.75 megabytes. Modern drives, 3.5 or 2.5 inches wide, are sold by the terabyte.
A hard drive stores data magnetically on rigid platters spinning at high speed, with heads on a moving arm reading and writing the surfaces. Any block can be fetched in any order, and nothing is lost when the power goes off. Disks became the main secondary storage for general-purpose computers from the early 1960s. The 350 had just one arm with two heads that shuttled between platters, but IBM's 1301 of 1962 used a comb of 48 heads, one per surface, gliding about six micrometres above the disk. The same year, the washing-machine-sized 1311 introduced removable disk packs that users could swap like reels of tape.
In 1973 IBM's Winchester design let heads land on a reserved strip of the disk when it spun down and lift off again at start-up, which made the mechanism much cheaper. A year later came the swinging arm actuator, invented at IBM's Hursley Labs in the UK; it became IBM's most licensed electro-mechanical invention ever and, with its filtration system, was eventually adopted by every hard drive maker. Platters shrank from 14 inches to eight in 1978, then to sizes that could replace floppy drives in the young PC market, and finally to today's 3.5 and 2.5 inches, helped by affordable rare-earth magnets.
In 1986 the most common drive held 10 megabytes, and by the end of that decade hard disks came in all but the cheapest computers. Early PC drives were often sold as add-ons under other brands, such as the Apple ProFile.
More than 224 companies have made hard drives, but consolidation left Seagate, Toshiba and Western Digital making most of them. Solid-state drives cost four to nine times more per bit, yet their revenue edged past hard drives in 2018 because they win on speed, power use, size and durability.
Source: Hard disk drive
