Editing Digital permanence (section)

==Types of storage==

===Solid-state memory devices===
Digital computers, in particular, make use of two forms of [[computer memory|memory]] known as [[random-access memory|RAM]] or [[read-only memory|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.  

* [[Magneti-core memory|Magnetic]], or ferrite core, data retention is dependent on the magnetic properties of iron and its compounds.
* [[Programmable read-only memory|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.

===Magnetic media===
[[File:magtape1.jpg|thumb|{{convert|7|in|cm|adj=on|0}} reel of {{convert|1/4|in|mm|0|adj=mid|wide}} audio recording tape, typical of consumer use in the 1950s–70s]]

[[Magnetic tape]]s 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 a maximum lifetime of about 50 years<ref name="Adelstein">Adelstein, Peter Z. "Permanence of Digital Information". Available at [http://www.ica.org/citra/citra.budapest.1999.eng/adelstein.rtf www.ica.org] {{Webarchive|url=https://web.archive.org/web/20040926035349/http://www.ica.org/citra/citra.budapest.1999.eng/adelstein.rtf |date=2004-09-26 }}.</ref> 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
* [[compact audio cassette|cassette tapes]]
* [[video tape|video cassette tapes]]

Magnetic disks and drums include a rotating magnetic medium combined with a movable read/write head.
* [[floppy disk]]s
* [[zip drive]]s
* [[hard disk]]s and drums

===Non-magnetic media===

* [[punched tape|punched paper-tape]]
* [[punched cards]]
* [[optical media]] (rotating media combined with a movable read/write head comprising a laser), such as:
** pressed [[CD-ROM]]s and [[DVD-ROM]]s
** [[Write once read many]] (WORM) media such as [[CD-R]], [[DVD±R]], [[BD-R]].
** Rewriteable media such as [[CD-RW]], [[DVD±RW]], [[BD-RE]].
** Some disc types can have multiple data layers for greater storage capacity.

===Printing technology===
Printing hard-copies of documents and images is 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 paper]]s, such as FAX rolls
* NCR and other ''carbon'' technologies
* [[ink-jet printer]]s
** wax-based inks e.g. DataProducts SI810
** water-based inks
** other bases
* mono [[laser printer]]s
* colour laser printers

===Financial Driven Resources===
A way of preserving digital content through means of [[financial trust]]s. The data is driven with financial investments typically assigned to a Trust Company which pay traditional storage providers to house data for long periods of time with the interest gained on the principal. In 2008 a series of companies such as LivingStory.com and Orysa.com started offering these services to store point in time accounting data and provide consumer archive services.

===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 (protocol)|BitTorrent]]
* [[networked backup]] services
* public archive repositories
* web-site archives
* financial trust resources