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What is a Data Storage Device?
http://www.hardwaretipsandtricks.com/articles/21/1/What-is-a-Data-Storage-Device/Page1.html
By Super Admin
Published on 11/21/2006
 
A data storage device is a device for recording (storing) information (data).

Data storage device

Recording can be done using virtually any form of energy. A storage device may hold information, process information, or both. A device that only holds information is a recording medium. Devices that process information (data storage equipment) may either access a separate portable (removable) recording medium or a permanent component to store and retrieve information.

Electronic data storage is storage that requires electrical power to store and retrieve data. Most storage devices that do not require visual optics to read data fall into this category. Electronic data may be stored in either an analog or digital signal format. This type of data is considered to be electronically encoded data, whether or not it is electronically stored. Most electronic data storage media is considered permanent (non-volatile) storage, that is, the data will remain stored when power is removed from the device. In contrast, electronically stored information is considered volatile memory

With the exception of barcodes and OCR data, electronic data storage is easier to revise and may be more cost effective than alternative methods due to smaller physical space requirements and the ease of replacing (rewriting) data on the same medium. However, the durability of methods such as printed data is still superior to that of most electronic storage media. The durability limitations may be overcome with the ease of duplicating (backing-up) electronic data.

Terminology
Devices that are not used exclusively for recording (e.g. hands, mouths, musical instruments) and devices that are intermediate in the storing/retrieving process (e.g. eyes, ears, cameras, scanners, microphones, speakers, monitors, projectors) are not usually considered storage devices. Devices that are exclusively for recording (e.g. printers), exclusively for reading (e.g. barcode readers), or devices that process only one form of information (e.g. phonographs) may or may not be considered storage devices. In computing these are known as input/output devices.

An organic brain may or may not be considered a data storage device.[1]

All information is data. However, not all data is information.

Data storage equipment
The equipment that accesses (reads and writes) storage information are often called storage devices. Data storage equipment uses either:

portable methods (easily replaced),
semi-portable methods requiring mechanical disassembly tools and/or opening a chassis, or
inseparable methods meaning loss of memory if disconnected from the unit.
The following are examples of those methods:

Portable methods
Hand crafting
Flat surface
Printmaking
Photographic
Fabrication
Automated assembly
Textile
Molding (process)
Solid freeform fabrication
Cylindrical accessing
Card reader/drive
Tape drive
Mono reel or reel-to-reel
Cassette player/recorder
Disk accessing
Disk drive
Disk enclosure
Cartridge accessing/connecting (tape/disk/circuitry)
Peripheral networking

Semi-portable methods
Hard drive
Circuitry with non-volatile RAM

Inseparable methods
Circuitry with volatile RAM
Chemical synapse

Recording medium
A recording medium is a physical material that holds data expressed in any of the existing recording formats. With electronic media, the data and the recording medium is sometimes referred to as "software" despite the more common use of the word to describe computer software. With (traditional art) static media, art materials such as crayons may be considered both equipment and medium as the wax, charcoal or chalk material from the equipment becomes part of the surface of the medium.

Ancient and timeless examples
 
Optical
Any object visible to the eye, used to mark a location such as a, stone, flag or skull.
Any crafting material used to form shapes such as clay, wood, metal, glass, wax.
Quipu
Any branding surface that would scar under intense heat.
Any marking substance such as paint, ink or chalk.
Any surface that would hold a marking substance such as, papyrus, paper, skin.
Chemical
DNA
Pheromone

Modern examples by energy used
 
Graffiti on a public wall. Public surfaces are being used as unconventional data storage media, often without permission.
Photographic film is a photochemical data storage medium
A floppy disk is a magnetic data storage medium
Hitachi 2.5 inch laptop hard drive. A hard drive is both storage equipment and a storage medium
Four major types of memory cards (from left to right: CompactFlash, MemoryStick, Secure Digital, and xD.
Picture of a Holographic Versatile Disc by Optware.Chemical
Dipstick
Thermodynamic
Thermometer
Photochemical
Photographic film
Mechanical
Pins and holes
Punch card
Paper tape
Piano roll
Music box cylinder or disk
Grooves (See also Audio Data)
Phonograph cylinder
Gramophone record
DictaBelt (groove on plastic belt)
Capacitance Electronic Disc
Magnetic storage
Wire recording (stainless steel wire)
Magnetic tape
Floppy disk
Optical storage
Photo paper
Hologram
Projected transparency
Laserdisc
Magneto-optical disc
Compact disc
Holographic versatile disc
Electrical
Semiconductor used in volatile RAM microchips
Floating gate transistor used in non-volatile memory cards

Modern examples by shape
A typical way to classify data storage media is to consider its shape and type of movement (or non-movement) relative to the read/write device(s) of the storage apparatus as listed:

Paper card storage
Punched card (mechanical)
Tape storage (long, thin, flexible, linearly moving bands)
Paper tape (mechanical)
Magnetic tape (a tape passing one or more read/write/erase heads)
Disk storage (flat, round, rotating object)
Gramophone record (used for distributing some 1980s home computer programs) (mechanical)
Floppy disk, ZIP disk (removable) (magnetic)
Holographic
Optical disc such as CD-ROM, CD-R, CD-RW, DVD, DVD-R, DVD-RW, DVD+R, DVD+RW, DVD-RAM, Blu-ray, Minidisc
Hard disk (magnetic)
Magnetic bubble memory
Flash memory/memory card (solid state semiconductor memory)
xD-Picture Card
MMC
USB Keydrive (also known as a "thumb drive")
SmartMedia
CompactFlash I and II
Secure Digital
SONY Memory stick (Std/Duo/Pro/MagicGate versions)
Solid state disk
Bekenstein (2003) foresees that miniaturization might lead to the invention of devices that store bits on a single atom.