Throughout her life, Susan Sontag filled her journals with lists of vocabulary (“integument,” “snap brim fedora,” “gruel,” “persiflage”) that she encountered in her reading and travels. These lists, and the journals that contain them, can be consulted much as researchers have always consulted literary archives: by turning up at the library—in this case, the Department of Special Collections at the Charles E. Young Research Library, at U.C.L.A.—filling out some forms, and waiting while the desiderata are fished from the stacks.

A Brazilian expression will sound familiar to anyone who has done research using a collection as vast as Sontag’s: “implacable archives.” When I reached Los Angeles in early January to work on my forthcoming biography of Sontag, I figured that three months would be plenty. For the past two years, I have been reading her work and travelling, mainly in Europe and Latin America, to meet the people who could help me reconstruct her implacable self.

It is hard—impossible—to think of a leading twentieth-century American writer whose life was as international. Even the famous expatriates of earlier generations tended to stay put in rather predictable places, such as London or Paris or Rome. London and Paris and Rome, for Sontag, were important, but so were São Paulo and Stockholm and Sarajevo.

In most of these places, a few days or a week have been enough. The time that I had in Los Angeles seemed positively luxurious. But the amount of material in the archives is so vast that I have despaired of ever looking at it all: hundreds of boxes of scraps of paper, photographs, journals, hotel bills, opera programs, love letters, drafts of published (and, as often as not, unpublished) manuscripts—bits and pieces that are thrilling to hold and which reveal things that can only be communicated by the original document.

You can see, in the handwriting, as never in a typed letter, how feverishly Sontag, given what looked like a death sentence when she was barely forty, sketched out the meditations on cancer that would become “Illness as Metaphor,” and how carefully, between those same pages, she guarded the prescriptions her doctor in Paris wrote for a course of chemotherapy then unthinkable in the United States. She could not, when she was writing the book, know that the lists of medicines scrawled on these pages would save her life.

Even when reading about less laden subjects, there is something melancholy about such close proximity to a person who existed and no longer does. These collections were once known as “literary remains”: this, after a lifetime of writing, is what remains.

Or it was.

A writer of Sontag’s generation—she was born in 1933—dealt for most of her life with paper. Her letters are real letters; her books were written with pens and typewriters. But, by the time she died, in 2004, these papers were fast becoming “remains.” Today, a letter makes a statement that it was not making twenty years ago: like telegrams, they are usually sent only for special occasions, and betray, by their very existence, information about their senders that they would not have conveyed before. (Often, that the sender is very old.)

The explosion of digital material in the past twenty-five years poses a particular challenge to the guardians of literary remains. I recently went into the recesses of U.C.L.A.’s research library to talk to Gloria Gonzalez, a twenty-four-year-old Mississippian. Gonzalez has found herself at the forefront of the movement to preserve this material since she began, while still a student, to deal with the Sontag archives. As I talked to her, my notes started looking like Sontag’s own, lines of unfamiliar words that defined a world new to me: “bit rot,” “forensic software,” “write blockers.”

“It’s actually not that new,” Gonzalez told me. “People have been using e-mail for twenty years. But it is new to archives. It’s not common for universities to look for this material.”

The material itself turns out to be two small hard drives that Gonzalez showed me in a cubicle behind the main special-collections reading room, each labelled with a Post-it note. “They are physical objects,” Gonzalez said, and in that sense are no different from the books and manuscripts that librarians have long collected and curated. But these objects are much more vulnerable than a traditional book. They are menaced by “bit rot,” in which the zeroes and the ones in which digital data is recorded mysteriously flip; by certain unstable storage devices (USB drives, for example); and by the more serious threat of technological obsolescence.

As she showed me pictures on Wikipedia of the computers that Sontag used—a PowerBook 5300, the computer that my mother bought me when I went to college—a PowerMac G4, and an iBook—I got the feeling so familiar from buying a new computer or phone, that twinge of embarrassment that the thing that only a few months ago felt so hip and ultramodern is already pathetically outdated.

The machines themselves are not in the library, however: future researchers will consult the material on a laptop in the reading room with software that displays it as Sontag would have seen it. This is to protect the physical files. “Every time you open an e-mail or a Word file, that material is changed,” Gonzalez said. “There are automatic updates or—for example, on a Word file—the date is changed to the date it was consulted, and you can’t see when she last worked on it.” (Sontag, in “On Photography,” wrote that to look at something is to change it.)

To preserve them, Gonzalez relies on techniques developed by law enforcement, an area known as digital forensics. The principal protection of a computer’s metadata is a write blocker, which allows the material to be seen without leaving any trace of the visitor. It is a fairly simple technical intervention. But the real threat comes from people who simply discard old computers, ignorant of their value.

Susan Sontag wrote seventeen thousand one hundred and ninety-eight e-mails, which will soon be available for consultation on a special laptop. I was given a special viewing at the library, and the experience gave me a queasiness that I have never felt during the years I have conducted historical research.