The "paperless office" has earned a proud place on lists of technological promises that did not come to pass. Surely, though, the more modest goal of he carbon-paperless office is within the reach of mankind? Carbon paper allows two copies of a document to be made at once. Nowadays, a couple of keystrokes can do the same thing with a lot less fuss.
    Yet carbon paper persists. Forms still need to be filled out in a way that produces copies. This should not come as a surprise. Innovation tends to create new niches( 合适的职业), rather than refill those that already exist. So technologies may become marginal, but they rarely go extinct. And today the little niches in which old technologies take refuge are ever more viable and accessible, thanks to the Internet and the fact that production no longer needs to be so mass; making small numbers of obscure items is growing easier.
    On top of that, a widespread technostalgia(技术怀旧 ) seeks to preserve all the ways people have ever done anything, simply because they are kind of neat. As a result technologies from all the way back to the stone age persist and even flourish in the modern world. According to What Technology Wants, a book by Kevin Kelly, one of the founders of Wired magazine, America's flintknappers (燧石) produce over a million new arrow and spear heads every year. One of the things technology wants, it seems, is to survive.
    Carbon paper, to the extent that it may have a desire for self-preservation, may also take comfort in the fact that, for all that this is a digital age, many similar products are hanging on, and even making comebacks. Indeed, digital technologies may prove to be more transient than their predecessors. They are based on the idea that the medium on which a file's constituent 0s and 1s are stored doesn't matter, and on Alan Turing's insight that any computer can mimic any other, given memory enough and time. This suggests that new digital technologies should be able to wipe out their predecessors completely. And early digital technologies do seem to be vanishing. The music cassette is enjoying a little renaissance, its very faithlessness apparently part of its charm; but digital audio tape seems doomed.
    So revolutionary digital technologies may yet discard older ones to the dustbin. Perhaps this will be the case with a remarkable breakthrough in molecular(分子的) technology that could, in principle, store all the data ever recorded in a device that could fit in the back of a van. In this instance, it would not be a matter of the new extinguishing the old. Though it may never have been used for MP3s and PDFs before, DNA has been storing data for over three billion years. And it shows no sign of going extinct.