The card index system; its principles, uses, operation, and component parts is a 1911 book by one R. B. Byles on the advantages of card indexes for businesses. It's an interesting read, if you are interested in the history of this technology.
The Introduction starts with the claim that "[r]oughly speaking, the world is divided into two classes: those who use the Card Index System and those who do not." The short book is meant to convince those who do not use the system to change their minds.
Monday, January 22, 2018
See also Guide to Using the Card Index and Gershom Scholem's Milon HaZohar Card Index – Yehuda Liebes. We are told that "[t]he notes are in the form of white cards, which Scholem stored in impeccable order in a long narrow wooden drawer that fit them perfectly, in his impressive writing desk (which today serves as the Scholem collections librarian's desk at the National Library)." It would be nice to know the format of the "cards" or, perhaps better, "slips."
It is more than likely that he learned this technique before he changed "Gerhard" to "Gershom."