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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 device 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 the contents of the Wikipedia we might like to keep around ... well, forever. 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. :; Data format : Data must be stored in a format which can be meaningfully accessed now and in the future. :; Technology reliance : If data requires a special program to view it, say, as an image, then software must also be available to both interpret the basic data file and also render it appropriately. In some cases, this might also require special hardware. :; Archival strategy : Data must remain available in the long term. :: At present a growing problem is the time taken to reproduce an archive, for instance following a hardware or system upgrade. Since the sheer volume of archive data continues to grow, new hardware is always required to maintain the archive and so regular migration of data to a new system must be performed on a regular basis. The time taken to migrate data is starting to approach the frequency of system upgrade such that archive transfer will become a continuous, never-ending processBurk, Alan; James Kerr; and Andy Pope. "The Credibility of Electronic Publishing". Available at web.mala.bc.ca . :; Digital rights management : Maintaining digital information in an accurate and accessible format over an extended retention period also must address the requirements of the authors' digital rights. :: In many cases the data may include proprietary information that should not be accessible to all, but only to a defined group of users who understand or have legally agreed to only utilize the information in limited ways so as to protect the proprietary rights of the original authoring team. Maintaining this requirement over decades can be a challenge that requires processes and tools to ensure total compliance. :; Reproducibility : Digital information must be able to be reproduced as originally intended or available. :: This is significant especially where the original data was produced on technology at a lower level than currently possible. For example, archivists try to maintain the distinction between listening to gramophone record played on a gramophone as opposed to a digitally cleaned version of the same recording though a modern hi-fi system. Given that individuals' personal data also seems to be growing at an alarming rateSweeny, Latanya. "Information Explosion. Available at privacy.cs.cmu.edu , these archiving issues affecting professional repositories will soon be manifest in small organisations and even the home. 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 media 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 maximum lifetime of about 50 yearsAdelstein, Peter Z. "Permanence of Digital Information". Available at www.ica.org . although this assumes optimal storage conditions; life expectancy can decrease rapidily depending on storage conditions and the resilience and reliability of hardware components.
Magnetic disks and drums include a rotating magnetic medium combined with a movable read/write head.
Non-magnetic media
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. Unfourtunately the permanence of printed documents cannot be easily discerned from the documents themselves.
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.
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