“Mag­netic tape, which stores most of the world’s com­puter back­ups, can degrade within a decade. Accord­ing to the National Archives Web site by the mid-​​1970s, only two machines could read the data from the 1960 U.S. Cen­sus: One was in Japan, the other in the Smith­son­ian Insti­tu­tion. Some of the data col­lected from NASA’s 1976 Viking land­ing on Mars is unread­able and lost forever.”