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2. General Preservation Factors

Preservation Masters and Access Copies

Many data carriers, especially modern high density formats, are, by their very nature, vulnerable. Additionally, there is always the risk of accidental damage through improper handling, malfunctioning equipment or disaster.

For the long term storage of many types of documents it is increasingly becoming necessary to review the strategies for preservation. One strategy that is widely used is the creation of access copies of documents. A poor quality copy can act as an adjunct to the catalogue to aid researchers to decide what documents they wish to study. A good quality copy may be acceptable for study in place of the original. The use of copies to reduce the frequency of access to the original document will reduce the stress on the original and help to preserve it. A clear policy about the classes of researchers allowed access to original documents - particularly fragile ones - will also help documents survive. It is clearly impossible to totally restrict access to originals but many users can perform their research using good quality access copies.

It is imperative, therefore, to have at least two copies of each document - one preservation master and one access copy. These should be stored in two different locations, ideally under different climatic conditions (see below). Several archives have established a policy to produce, in addition to the preservation master, an additional safety copy. Computer centres have established similar policies to safeguard the data in their care.

Archive quality microfilm, used by many institutions both as a preservation and a high quality access medium, is being supplemented by digital storage systems using optical discs and magnetic tapes as the carrier. A further advance being considered by a number of institutions is the self­controlling and self­regenerating digital mass storage system. This is currently being tested as a medium for the safeguarding of some collections of audiovisual documents. This kind of concept may also provide a solution for the major problem of the safeguarding of electronic documents. Such mass storage systems are, at the same time, an indispensable pre­requisite for the functioning of all kinds of services in the forthcoming information age, for example "digital libraries" and "video on demand".

The price of mass storage systems is relatively high at present but will soon come within the reach of average budgets. Contrary to fears expressed by some, this concept does not call exclusively for huge, centralized stores: it will also allow individually tailored solutions for smaller applications. Thus, such systems could also be a solution for the preservation of documents in countries with adverse climatic conditions.

While in hot and humid environments conventional preservation techniques may be inappropriate due to the notorious lack of funds for the proper air-conditioning of storage areas, mass storage systems, requiring relatively small floor space, can be effectively airconditioned at a lower cost. As an example, a cabinet available from one typical system, occupying one square metre of floor space, can hold the equivalent of over one million pages of A4 text.

Obsolescence of Hardware

With development of technology, recording systems, ie the carriers together with the necessary recording and replay equipment, have become increasingly sophisticated. Even for textual materials, the almost universal use of word processors can create unexpected difficulties. At the same time, the (commercial) lifetime of systems has become increasingly shorter. While for traditional audiovisual formats such as analogue tape the lifetime of the tape was of predominant interest, the future availability of suitable and functioning replay equipment is becoming the burning issue for several modern formats. In the computer world, the availability of dedicated drives has always been of greater concern than the stability of the respective carriers. The situation is additionally aggravated by the obsolescence of dedicated software and operating systems. Several audio archives are now systematically transferring their holdings into self-controlling and self-regenerating mass storage systems (see above) to escape the vicious circle of ever decreasing life spans of carriers and their dedicated hardware. It has become apparent that, in setting up strategies for the safeguarding of both audiovisual and electronic documents, the future migration has to be taken into account.

Maintenance of Equipment

With all machine readable documents, the performance of recording and replay equipment is a central factor in the safeguarding of data. Great efforts have to be made to keep equipment in the best possible condition. To this end, many audio-visual archives and computer centres have their own service departments employing well trained personnel. In a time of ever increasing sophistication of equipment, however, there is an increasing amount of work that has to be done by specialists from outside. When out sourcing such jobs to third parties, the essential role of machine maintenance for the safeguarding of the collection has to be kept in mind.

Climatic Conditions

To ensure a long life for the polymers carrying the information in storage, it is necessary to control the climatic conditions in the store. The basic requirement is for stable temperatures and stable humidity levels. Large variations in either parameter will accelerate the decay processes.

High temperatures will accelerate the decay processes; cooler temperatures will slow them. Similarly, high levels of humidity in the storage areas will encourage hydrolysis and, if above 65% RH, will encourage the growth of moulds and fungi. It is common knowledge that many polymers are best stored at low temperatures. It is less commonly known that humidity also must be controlled. The problem for many collections is that is relatively easy to keep the temperature in the storage areas stable but controlling the humidity level is more difficult and expensive.

As the temperature drops the air can hold less moisture and the relative humidity rises. If a store is cooled without simultaneously controlling humidity, there is a danger that moulds and fungi will be encouraged to grow. These growths will not only eat away at paper and other natural polymers but will also make machine readable carriers - magnetic tapes, optical discs etc - unplayable and possibly damaging the equipment. If it is not possible to keep humidity below 65%RH when the store is cooled, it would be better to set a higher, but stable, target temperature that will ensure that humidity is kept stable and below 65%RH. The penalty, however, will be a shorter life for the carriers.

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