A binary switch has been proposed to steer two bubble streams to either cross or bypass each other under external electronic control. A linear array of bubble shift register loops can be linked together by these flow-steering switches to form a storage structure which will be called a bubble ladder. It is shown that the ladder can alternate between two data structures-LIFO and FIFO. For storage units based on the ladders, a scheme is developed to rearrange data items according to recency of usage for improving average access time. © 1975, IEEE. All rights reserved.