Digital permanence addresses the history and development of digital storage techniques, specifically quantifying the expected lifetime of data stored on various digital media and the factors which influence the permanence of digital data. It is often a mix of ensuring the data itself can be retained on a particular form of media and that the technology remains viable. Where possible, as well as describing expected lifetimes, factors affecting data retention will be detailed including potential technology issues. Since the inception of computers, a key concept differentiating computers from other calculating machines has been their ability to store information. Over the years, various hardware devices have been designed to store ever larger quantities of data. With the development of the Internet the quantity of information available appears to continue to grow at an ever increasing rate often characterised as an Information Explosion. As information stored on traditional media such as hand-written documents, printed books, photographic images and the likes is being replaced by digital files so our social and cultural legacy to future generations will depend more and more on the permanence of digital information. However, not all this information is worth saving for any length of time; sometimes its value can be very short-lived. Other data, such as legal contracts, literature, scientific studies, are frequently expected to last for centuries. This article describes how reliable different types of storage media are at storing data over time and factors affecting this reliability. Librarians and archivists responsible for large repositories of information take a deeper view of electronic archives. Given that individuals' personal data also seems to be growing at an alarming rate, these archiving issues affecting professional repositories will soon be manifest in small organisations and even the home.
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.
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
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 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.
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.
A way of preserving digital content through means of financial trusts. 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.
