Magnetic storage is commonly used for storing large amounts of data such as videos, text and images. All magnetic storage works in a similar way, recording data using tiny magnetised dots. Magnetic fields made by small electromagnets are then used to create, read and erase these dots. Three common types of magnetic storage, also called magnetic memory, are tapes, disks and hard drives.
Tapes were one of the first types of magnetic storage, using a coated ribbon wrapped around two wheels. Magnetised dots or particles are arranged along the length of a long plastic strip which has been coated with a magnetisable layer, similar to the technology used for audio and video tapes.
Of this type of magnetic storage there are two choices; reel-to-reel or cartridge. The cartridge typically has hundreds of feet of magnetic tape and is usually used in personal computers. Reel-to-reel tapes have several thousand feet wrapped around spools. This type of magnetic storage is called a tape drive and is used on mainframes. A tape drive works like a tape recorder with two heads. One head reads the information, the other writes. As the tape winds over the head, data is either written or read. Tapes are an inexpensive type of magnetic storage but they are slow because you must either rewind or advance the tape to where the data that is needed starts.
Removable media like floppy disks transfer small amounts of data either between computers or to backup disks. Nearly all computers used to have a floppy disk drive, but they've since been replaced for the most part by CDs and DVDs. In these disks, magnetised dots are arranged in circles on the surface of the disc (plastic, metal or glass) that has a magnetisable coating. A floppy disk drive reads and writes to a small round piece of metal-coated plastic much like an audio cassette. Magnetic disks are coated with iron oxide, which is ferromagnetic, meaning it becomes permanently magnetised if you expose it to a magnetic field.
Hard drives can store vast amounts of data and are called random access devices, which means you don't have to search through the hard drive to find the data before retrieving it. Hard drives store data on rotating metal or glass disks (platters). Most computers have a hard drive built inside. These drives are the main storage device for most computers because they provide instant access to files at high speeds. There are also portable hard drives, which are outside the computer and connected using a USB or similar connection. Portable hard drives are typically used to transfer data between computers.