Introduction
Computer systems need to store data in digital format. One of the most widely used types of digital data storage is magnetic storage. This refers to any type of data storage using a magnetized medium. Digital data consists of binary information, which is data in the form of zero and ones. There are two types of magnetic polarities, each one used to represent either zero or one.

Several types of magnetized media are used in computer systems, including magnetic tape, floppy disks and hard disk drives. The basic approach to magnetic data storage, however, is very similar for the different types of media. A read-write head moves very close to the magnetic surface - the distance is often no more than tens of nanometers. The head is able to detect and modify the magnetization of the material. The magnetic surface is divided into very small regions, each of which has a mostly uniform magnetization. As the head moves relative to the surface, the changes in magnetization from region to region are detected and recorded as zeros and ones. Different technologies vary in how the head moves relative to the surface of the media and how the regions on the media are organized, but the basic principle is the same.

Magnetic storage is a form of non-volatile storage. This means that the data is not lost when the storage device is not powered. This is in contrast to volatile storage, which is typically used for the main memory of a computer system. Volatile storage requires a constant power supply - when a computer system is turned off, the data is lost.

Magnetic storage is widely used because it is relatively cheap in comparison with other storage technologies. Magnetic storage is read-write, which makes it possible to re-use the storage capacity over and over again by deleting older data. The storage capacity is also very large, making it attractive for storing very large amounts of data. The major limitation of magnetic storage is that accessing the data can be quite slow. As a result, most computer systems use magnetic storage for non-volatile storage of large amounts of data (typically in a form of a hard-disk drive) but a different type of storage for system memory, such as read-only memory (RAM), which is much smaller but can be accessed much faster.

Types of Magnetic Storage Devices

Magnetic tape is one of the older types of magnetic storage media. The magnetic tape recorder was invented in 1928 and was primarily used for analog audio recordings. Before music CDs were introduced in the 1980s, portable music devices used magnetic tape in the form of music cassettes. Early computers adapted this technology to store digital information. One of the major weaknesses is that information on a tape can only be accessed in a very sequential fashion. This is fine if you want to listen to a whole music album in sequence, but computer systems typically need to access data in a non-sequential manner. For magnetic tape, this means you may need to fast forward through a lot of tape to get to a specific piece of data. While magnetic tape is a very cheap way to store data, the very slow access to the data meant that it was primarily used for creating backups of data in case older forms of storage failed. Tape backup systems are still in use today, but their importance has greatly declined with the advance of cheap, large capacity hard-disk drives.