External storage

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In computing, external storage comprises devices that store information outside a computer. Such devices may be permanently attached to the computer, may be removable or may use removable media.

Types of external storage[edit]

Magnetic storage[edit]

Optical storage[edit]

Optical storage devices have media that use laser light technology for data storage and retrieval.

Compact disc[edit]

Types of Compact Discs (CDs) include:

  • CD-ROM: (Compact Disc Read Only Memory) It can only be read through the drive. And are usually manufactured by in bulk by a stamp type system.
  • CD-R: (Compact Disc Recordable) was invented in the 1990s. Using CD-R, it is possible to write data once on a disc at home without the stamping equipment required for CD-ROMs. These are considered write once, read many disks.
  • CD-RW: (Compact Disc Re-Writable) same as the CD-R but can be erased and reused. There is a limit on how many times a CD-RW can be written. Presently this limit is 1000 times. CD-RW drives are compatible with CD-ROM and CD-R.


DVD stands for Digital Versatile Disc. Its speed is much faster than CD but not as fast as hard disk. The standard DVD-5 technology has a storage capacity of 4.7 GB per layer; most DVDs have a single layer but up to four layers are specified. Also DVD storage capacity changes with recording format.


Blu-ray storage capacity is up to 50 gigabytes (or even 100 GB) of data.[1] The Blu-ray Disc (BD) is a digital optical disc format. It was originally created to take the place of the DVD format due to its expanded storage capacity. The name "Blu-ray" is derived from the use of a blue laser that is used to read the disc. This would be in contrast to the red laser used to read DVD Discs.


M-Discs are available as DVD or Blu-ray discs.

Flash memory devices[edit]

Memory card[edit]

Memory cards are flash memory storage media used to store digital information in many electronics products. The types of memory cards include CompactFlash, PCMCIA, secure digital card, multimedia card, memory stick etc.

Memory stick[edit]

Sony introduced memory stick standard in 1998. Memory stick is an integrated circuit designed to serve as a storage and transfer medium for digital data. It can store data in various form as text, graphics, digital images etc. transfer of data is possible between devices having memory stick slots. Memory sticks are available in various storage sizes ranging from 4 MB to 64 MB. The dimensions of a memory stick are 50 mm long, 21.5 mm wide and 2.8 mm thick (in case of pro format). The transfer speed of memory stick is 160 Mbit/s.

USB drives[edit]

A USB flash drive, also variously known as a, thumb drive, pen drive, jump drive, disk key, disk on key, flash-drive, memory stick or USB memory,[a] is a data storage device that includes flash memory with an integrated USB interface


  1. ^ "Blu-ray Disc for Data". Blu-ray Disc Association. Blu-ray Disc Association (BDA). Retrieved 27 September 2015.