The electronic archive at Washington University in St. Louis, Mo., is a library without walls for books without pages, perhaps the world's largest public computerized information source and the most significant change in the nature of the public library in centuries.
The archive is housed in a small computer on a folding table. A modem serves in lieu of a library card. The database stored in the computer takes the places of actual books. An average of 45,000 people query it every day; none of them has to set foot in St. Louis.
But there recently was a problem. The archive vanished.
The computer's memory failed.
For some computer scientists and library specialists, the fragility of the St. Louis archive, which has since been painstakingly restored, is a cautionary tale.
Dozens of even more comprehensive electronic libraries are being planned. But experts worry that reliance on electronic archives may make humanity's hard-won knowledge more vulnerable and expose it to unexpected risks of technological obsolescence.
Computer equipment becomes obsolete so quickly that it may be impossible for historians of the next generation to study today's electronic records, documents or databases.
As computers make it easier to store, catalog and retrieve information, the information itself is becoming more fragile.
Conventional type can withstand all but destruction of the page on which it is printed, but it only takes a stray magnetic field to erase an electronic file forever.
In St. Louis, the books of that virtual library were as vulnerable to a flipped bit or a power surge as monastic scrolls were to the barbarian's torch.
Another library is being assembled by Bill Gates, chairman of Microsoft Corp. On Tuesday, his privately owned Corbis Corp. ++ bought one of the largest, most respected collections of photographs and drawings, the Bettmann Archive. When digitized, its images can be sent to anyone with a computer and modem.
For researchers and archivists awash in hard-copy information, the immediate promise of electronic archives and libraries is a liberating one.
The National Archives houses about 6 billion documents, 7 million pictures, 118,000 movie reels and 200,000 recordings.
The 65-acre Library of Congress, the world's largest library, houses more than 107 million items, ranging from the papers of 23 U.S. presidents to one of only three existing perfect copies of the Gutenberg Bible.
Confronted with such perishable mountains of material, the Library of Congress joined this spring with 14 other major research libraries to begin a national digital library.
As a start, they hope to have 5 million digital documents available to the public through the Internet and on CD-ROM by decade's end.
The aim is to drastically lower the cost of warehousing books, manuscripts, photographs, maps, motion pictures and sound recordings, while dramatically broadening public access to even the most obscure historical collections.
With computerized indexes, scholars might even discover everything that is actually stored on the hundreds of miles of shelves and file drawers in the National Archives.
There is also the hope that electronic storage can solve the preservation problems that make present-day archival efforts a losing race with time.
The best-tended paper will crumble. Film will dissolve. Recording tape will quickly lose its voice. Even museum-quality photos eventually will fade away.
Digital offers the ability to make perfect copies of any document, image, audio recording or film. It means that librarians can consolidate the different elements of their collections into one form, such as a CD-ROM disk.
But even if libraries go completely digital, others worry they will not escape all the problems that plague them now.
Digital archives will still last only as long as the physical material on which they are stored. Computer tape, floppy disks and hard drives last only a few years. Even sturdy CD-ROMs barely last a generation.
"The preferred media on which this digital information is stored -- disk, tape and even CD-ROM -- have far shorter shelf lives than acid-free paper or microfilm," notes Jeff Rothenberg, an expert on computer storage and longevity at the RAND Corp., and Avra Michelson, an information storage expert, in the American Archivist.
While that may not be so different from the preservation problems archivists already face, digital storage adds a new, and unsettling, wrinkle.
Once a document is converted to silicon storage, its meaning is submerged in a so-called "bit-stream" of electronic digital zeros and ones. The resulting digital file is meaningful only to the software that created it.
The stored bits in a digital file could represent a letter of the alphabet, a pixel dot in an image, an audio signal or a number.
There is no way to retrieve it, or to be certain if it even exists, except by reading it with the proper software and computer hardware.
"It is not a document anymore," says Mr. Rothenberg. "It is just a bunch of gibberish until you run the software that interprets it and puts the document up in front of you."
Even if the computer program that created the files is preserved, there may be no surviving compatible computer that can run it.
Already the National Archives has to contend with an electronic Babel of nine-track magnetic tapes, computer tape cartridges, analog videodiscs and audio compact discs.
Last year, the archives started accepting government documents recorded on optical CD-ROM computer disks.
"The thing that is really troubling about a computer tape is that you can't really tell something is wrong until you try to read it," said Fynette Eton, acting director of the Center for Electronic Records at the National Archives.
For now, conservators at the Library of Congress and the archives are taking a judicious approach toward storing their collections on computer.
The materials they want most to save are some of their most irreplaceable items. So there are no plans to throw away a manuscript or a photograph once it has been copied electronically.