"Digital preservation" is revealed by our work as a non-unitary concept: it depends upon what is digitised, the period over which the preserved material is anticipated to be of use, and the future end uses to which it is believed the material may be put. Clearly, memory institutions have the longest view, since they are the storehouses of reserved physical materials from, in some cases, hundreds of years in the past. However, even here, question of which institutions need to retain digital archives and which may draw upon those archives is a significant question. On the other hand, our work in industry suggests that the useful time period over which digital objects may be seen as useful will depend mainly upon two factors: the lifetime of a product and legal requirements for preservation. In the case of TV sets, the production lifetime is quite limited, with new models coming out every two or three years, but in the case of health products from the same organization, legal requirements relating, for example, to testing may require records to be maintained for a much longer period of time. Even then, the expenditure has to be justified by the business benefits.