When I was in college, I studied German. My professor asked us to buy a box of cards that were basically 3x5 cards with notched edges. He called them our computer system. You would make notes on the card and then cut out the appropriate notches on the edges. Each notch was recorded on an index card. Then if you wanted to search for a topic, you would find the reference to the appropriate notch on the index card, stick a thin metal rod through that notch on all cards, shake the desk and the appropriate cards would fall out. You could repeat this operation any number of times to fine tune your query.
The cards came with a nice box where you could store your stash of cards.
I found a reference to these type of cards on Wikipedia. They were known as Needle Cards. You can find the Wiki article here.
I did find this "computer system" useful for research. I probably should have used it in my other classes ... especially History.