Leather Digital Camera

Digital permanence

Types of storage

Solid-state memory devices

Digital computers, in particular, make use of two forms of memory known as RAM or ROM and although the most common form today is RAM, designed to retain data while the computer is powered on, this was not always the case. Nor is active memory the only form used; passive memory devices are now in common use in digital cameras.

Magnetic, or ferrite core, data retention is dependent on the magnetic properties of iron and its compounds.

PROM, or programmable read-only memory, stores data in a fixed form during the manufacturing process, with data retention dependent on the life expectancy of the device itself.

EPROM, or erasable programmable read-only memory, is similar to PROM but can be cleared by exposure to ultraviolet light.

EEPROM, or electrically erasable programmable read-only memory, is the format used by flash memory devices and can be erased and rewritten electronically. These devices tend to be extraordinarily resilient; in a 2005 destructive test, a USB key survived boiling in a custard pie, being run-over by a truck and fired from a mortar at a brick wall. Although physically damaged after the final test, some deft soldering restored the device and data was successfully retrieved.

Magnetic media

Magnetic tapes consist of narrow bands of a magnetic medium bonded in paper or plastic. The magnetic medium passes across a semi-fixed head which reads or writes data. Typically magnetic media has maximum lifetime of about 50 years although this assumes optimal storage conditions; life expectancy can decrease rapidly depending on storage conditions and the resilience and reliability of hardware components.

magnetic tape reels

magnetic stripe cards

magnetic cards

cassette tapes

video cassette tapes

Magnetic disks and drums include a rotating magnetic medium combined with a movable read/write head.

floppy disks

zip drives

hard disks and drums

Non-magnetic media

punched paper-tape

punched cards

optical media (rotating media combined with a moveable read/write head comprising a laser), such as:

pressed CD-ROMs

WORMs, CD-R

DVDs

multi-layer DVDs

Printing technology

Although not a digital storage medium in itself, printing hard-copies of documents and images remains a popular means of representing digital data and possibly acquires the qualities associated with original documents especially their potential for endurance. More recent advances in printer technology have raised the quality of photographic images in particular. Unfortunately the permanence of printed documents cannot be easily discerned from the documents themselves.

wet-ribbon inked printers

heat sensitive papers, such as FAX rolls

NCR and other carbon technologies

ink-jet printers

wax-based inks eg. DataProducts SI810

water-based inks

other bases

mono laser printers

colour laser printers

Soft storage technology

The short-comings of some storage media is already well recognised and various attempts have been made to supplement the permanence of an under-lying technology. These "soft storage technologies" enhance their base technology by applying software or system techniques often within quite narrow fields of data storage and not always with the explicit intention of improving digital permanence.

RAID systems

Distributed systems, such as bitTorrent

networked backup services

public archive repositories

web-site archives

See also

UK Digital Archive Strategy

References

^ Burk, Alan; James Kerr; and Andy Pope. "The Credibility of Electronic Publishing". Available at web.mala.bc.ca

^ Sweeny, Latanya. "Information Explosion. Available at privacy.cs.cmu.edu

^ Sky One

^ Adelstein, Peter Z. "Permanence of Digital Information". Available at www.ica.org.

Categories: Digital technology
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