Vinyl records are circular because it's an efficient use of space: the grooves that encode the music are laid out in a spiral on the disc, so that the needle only has to move as far as the disc's radius to read the entire thing. Before this clever idea was thought of, the grooves were instead laid out in a straight line, and every LP was a narrow rectangle more than a thousand feet long. To flip an album to side b at least two people were needed, one at each end, coordinating via shouted instructions.

For the cassette tape they revived this idea with the genius addition of rolling the rectangle up so it would fit inside the tape player.