Before computers came along the way you looked up a book was using the card catalog. The card catalog used to be in the main reading room at the Library of Congress.
I remember using it when I was doing research when I was in college. I especially remember doing a paper on The War of 1812. I used the card catalog and got books about it. Several were from the mid 1840s. I thought it was so cool to be holding in my hand a book that was over 130 years old.
Here are a few pictures of the catalog. It is stored just off the main reading room. It is still used. You can also see that not all of the books in the Library of Congress are in English. Many in fact are in other languages as you can see from the the last picture. I did over hear one of the librarians say that because of budget cut backs fewer foreign language books are being purchased.