External storage
In computing, external storage refers to non-volatile data storage outside a computer's own internal hardware, and thus can be readily disconnected and accessed elsewhere. Such storage devices may refer to removable media, compact flash drives, portable storage devices, or network-attached storage. Web-based cloud storage is the latest technology for external storage. In recent years, analysts have noted that the rapid growth of cloud-based external storage has shifted emphasis from physical media toward distributed, service-based architectures used by both consumers and enterprises.
History
Today the term external storage most commonly applies to those storage devices external to a personal computer. The terms refer to any storage external to the computer.Storage as distinct from memory in the early days of computing was always external to the computer as for example in the punched card devices and media. Today storage devices may be internal or external to a computer system.
In the 1950s, introduction of magnetic tapes and hard disk drives allowed for mass external storage of information, which played the key part of the computer revolution. Initially all external storage, tape and hard disk drives are today available as both internal and external storage.
In the 1964 removable disk media was introduced by the IBM 2310 disk drive with its 2315 cartridge used in IBM 1800 and IBM 1130 computers. Magnetic disk media is today not removable; however disk devices and media such as disc drive">optical disc">disc drives and optical discs are available both as internal storage and external storage.
Earlier adoption of external storage
As a consequence of rapid development of electronic computers, capability for integration of existing input, output, and storage devices was a determinant factor in their adoption. IBM 650 was a first mass-produced electronic computer that encompassed wide range of existing in technologies for input-output and memory devices, and it also included tape-to-card and card-to-tape conversion units. Earlier "transportable personal storage" was introduced by IBM's 2315 disk cartridges, which were used in IBM 1800 and IBM 1130 computers. Operating systems of the earlier 1960s provided a general-purpose file system for external storage, which included hierarchical directories, symbolic links, and access control to time-sharing mainframe computers. Some of such earlier examples include UNIVAC, MULTICS, and UNIX.Types of external storage
Paper data storage
Magnetic storage
Optical storage
Optical storage devices have media that use laser light technology for data storage and retrieval.Compact disc
Types of Compact Discs include:- CD-ROM: It can only be read through the drive. And are usually manufactured by in bulk by a stamp type system.
- CD-R: 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: 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 1,000 times. CD-RW drives are compatible with CD-ROM and CD-R.
DVD
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
Blu-ray storage capacity is up to 50 gigabytes of data.The Blu-ray Disc 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.