Mass storage

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This article describes mass storage in general. For the USB protocol, see USB mass storage device class.

In computing, mass storage refers to storage of large amounts of information in a persisting and machine-readable fashion. Storage media for mass storage include hard disks, floppy disks, flash memory, optical discs, magneto-optical discs, drum memory, magnetic tape, punched tape (historic) and holographic memory (experimental). It does not include random access memory, which is volatile i.e. it loses its contents after power loss.

A drive is a peripheral device attached to a computer to access the information stored on a mass storage medium. In some types of drive, the storage medium is permanently sealed inside the device. In others, the medium can be replaced with varying levels of difficulty. Also, some drives with permanently attached media are designed to be portable as a whole.

Mass storage devices are characterized by:

Transfer speed
Seek time
Cost
Capacity

Today, magnetic disks lead on all four and have come to be the dominant mass storage medium.

1 Usage
2 Mass storage types
3 References
4 See also

[edit] Usage

Mass storage devices used in desktop and most server computers typically have their data organized in a file system. The choice of file system is often important in maximizing the performance of the device: general purpose file systems such as NTFS and HFS, for example, do poorly on slow-seeking optical storage such as compact discs.

Some relational and flat databases can be also used directly on mass storage devices without an intermediate file system or storage manager. The Oracle and MySQL databases, for example, can be deployed directly on direct-access devices.

Archive formats—sequential formats which pack data end-to-end—are more common on removable media used in batch archival because they are simpler to stream than file systems and are more portable.

On embedded computers, it is common to memory map the contents of a mass storage device (usually ROM or flash memory) so that its contents can be traversed as in-memory data structures or executed directly by programs.

[edit] Mass storage types

The design of computer architectures and operating systems are often dictated by the mass storage and bus technology of their time. Desktop operating systems such as Windows are now so closely tied to the performance characteristics of magnetic disks that it is difficult to deploy them on other media like flash memory without running into space constraints, suffering serious performance problems or breaking applications.