Magnetic storage

Magnetic storage is a method of saving data on a magnetized medium. It is a form of non-volatile memory, meaning the information remains stored even without power. This technology is essential for modern computing and media production. In computers, it is usually called magnetic storage. In audio and video fields, it is often called magnetic recording.

Common examples include hard disk drives (HDDs), magnetic tape, floppy disks, and the magnetic stripes on credit cards.

To understand how it works, we must look at the read-and-write head. This device moves extremely close to a magnetic surface, often just tens of nanometers away. The head stays from touching the surface by riding on an air bearing. This is a thin layer of air that moves at or near the speed of the platter. The head consists of a slider that keeps it hovering safely.

A write head uses a strong local magnetic field to magnetize specific regions. A read head then detects these magnetic patterns to retrieve the data.

At a microscopic level, the magnetic surface is divided into small regions called magnetic domains. These domains have a mostly uniform magnetization. Each domain acts as a magnetic dipole that generates a magnetic field. Because the material is polycrystalline, each region is made of a few hundred magnetic grains. These grains are typically 10 nm in size. In digital recording, these domains represent binary data, using two stable states to signify 0 or 1.

There are different ways to arrange these magnetic domains. Older hard disk designs used longitudinal recording, where domains were oriented horizontally and parallel to the disk surface. Newer disks use perpendicular recording. In this method, the domains stand upright, which allows for much closer spacing between them. This change helps increase data density.

The materials used have also evolved. While older drives used iron(III) oxide (Fe2O3), modern disks use a cobalt-based alloy to ensure reliable storage.

The history of magnetic recording spans over a century. In 1878, Oberlin Smith filed a patent for recording audio on a wire. He later publicized this idea in 1888. In 1898, Valdemar Poulsen invented a device that recorded signals on a wire wrapped around a drum. He demonstrated this at the Paris Exposition in 1900. Later, in 1928, Fritz Pfleumer developed the first magnetic tape recorder. Early devices were designed for analog signals, but modern devices almost exclusively use digital data.

Different types of magnetic recording serve different purposes. Analog recording uses a continuous distribution of magnetization on a medium, like polyester film tape with magnetic particles. Digital recording, however, only requires two stable magnetic states. There is also magneto-optical recording, which uses a laser to heat the medium locally. This allows a small magnetic field to switch the magnetization. A famous example of this is the Sony MiniDisc. Another specialized type is domain propagation memory, or bubble memory. This uses stable cylindrical domains and is used in space and aeronautics because it is resistant to shock and vibration.

Magnetic storage systems vary in how they access information. Sequential access memory requires moving through the medium in order, such as winding magnetic wire. Random access memory allows for much faster retrieval of specific locations. Hard disks are very fast, typically accessing data in less than 10 ms. In contrast, magnetic tapes can take as much as 100 seconds to find a specific spot.

This makes hard disks better for quick tasks and tapes better for high-capacity archives.

Future developments aim to make storage even faster and more efficient. Researchers are working on magnetoresistive random-access memory, known as MRAM. This uses the tunnel magnetoresistance (TMR) effect to store data in magnetic bits. MRAM is non-volatile and uses very little power. Scientists like Aleksei Kimel are also researching the use of terahertz radiation for writing data. Using terahertz radiation could make writing 50 times faster than current methods. It also generates almost no heat, which would reduce the need for cooling systems.