Kryder’s Law: The Number of Bits Stored on a Magnetic Disk

Chapter 12 explains Kryder’s law, which describes the exponential growth of magnetic disk storage capacity and areal density from 1956 to about 2012, doubling roughly every 13 months—faster than Moore’s law. The first commercial hard disk, introduced by IBM in 1956, stored 5 MB. Advances such as giant magnetoresistance (GMR) read/write heads, perpendicular magnetic recording, and heat-assisted magnetic recording (HAMR) enabled dramatic increases in density and capacity. However, after 2012, growth slowed due to physical and technological limits and competition from solid-state memory, which offered faster speeds and no moving parts. Today, HDDs remain relevant for large-scale storage, cloud services, and archival purposes, with capacities reaching 30 TB using HAMR and microwave-assisted magnetic recording (MAMR). Toshiba and Seagate lead in developing next-generation drives, while emerging research on altermagnetic materials may offer future breakthroughs. Magnetic storage, though no longer dominant, continues to evolve for high-capacity applications.