For the youngsters on here: how one found items in dead-tree libraries before computers came around. These are called a "card catalog". They were familiar objects for generations of people worldwide.

I searched the web but picked the Wikipedia page as one of the best resources on the subject. Some other pages you might enjoy:

Library of Congress - How to use the card catalog https://guides.loc.gov/card-catalog/using-the-card-catalog Developer of an early, widely used computer standard https://en.wikipedia.org/wiki/Henriette_Avram https://www.allpurposeguru.com/2013/10/card-catalog-birth-an...