Mass_storage

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

In computing, mass storage refers to the 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, magnetic tape, drum memory, punched tape (mostly historic) and holographic memory (experimental). Mass storage includes devices with removable and non-removable media. It does not include random access memory (RAM), which is volatile in that it loses its contents after power loss.

Mass storage devices are characterized by:

• Sustainable transfer speed
• Seek time
• Cost
• Capacity

Today, magnetic disks are predominant storage media in personal computers. Optical discs, however, are almost exclusively used in the large-scale distribution of retail software, music and movies because of the cost and manufacturing efficiency of the moulding process used to produce DVD and compact discs and the nearly-universal presence of reader drives in personal computers and consumer appliances.Taylor, Jim. DVD FAQ. Retrieved on 2007-07-08. “In 2003, six years after introduction, there were over 250 million DVD playback devices worldwide, counting DVD players, DVD PCs, and DVD game consoles.” Flash memory (in particular, NAND flash) has an established and growing niche in removable storage and on portable devices such as notebook computers and cell phones because of its portability and low power consumption.Gonsalves, Antone (23 May 2007), "Micron predicts flash memory will replace disk drives", EETimes, <http://www.eetimes.com/news/semi/showArticle.jhtml?articleID=199701290>.Flash Drives: Always on the Go, Without Moving Parts. New York Times (2005-02-17). Retrieved on 2008-02-24..

The design of computer architectures and operating systems are often dictated by the mass storage and bus technology of their time.Patterson, Dave (June 2003), "A Conversation With Jim Gray", ACM Queue 1 (4), <http://www.acmqueue.org/modules.php?name=Content&pa=printer_friendly&pid=43&page=1>. (A discussion of recent trents in mass storage.) 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.

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) tend do poorly on slow-seeking optical storage such as compact discs.

Some relational databases can also be deployed on mass storage devices without an intermediate file system or storage manager. Oracle and MySQL, for example, can store table data directly on raw block devices.

On removable media, archive formats (such as tar archives on magnetic tape, which pack file data end-to-end) are sometimes used instead of file systems because they are more portable and simpler to stream.

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.

References

See also

• Data storage for general overview of storage methods
  • Computer data storage for storage methods specific to computing field
    • Disk storage for both magnetic and optical recording of disks
    • Magnetic tape data storage
    • Computer storage density
    • List of device bandwidths
    • Solid-state drive
    • RAM disk

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