Imagine a library filled with thousands of books on every subject imaginable. Shelves full from floor to ceiling: Fiction, nonfiction, auto-mechanic manuals. How do you find the book you need?
You pull out a tiny drawer and page through hundreds of index cards — one for each of the books in the library — until you find the one you want. You jot down a decimal number with a tiny pencil and head off into the stacks.
For anyone born before 1990, that’s the way libraries worked. Before computers came on the scene, the card catalog was king. Its orderly drawers held all the answers, one 3-by-5 card at a time.