The running time of programs in a paging machine generally increases as the store in which programs are constrained to run decreases. Experiment, however, have revealed cases in which the reverse is true: a decrease in the size of the store is accompanied by a decrease in running time. An informal discussion of the anomalous behavior is given, and for the case of the FIFO replacement algorithm a formal treatment is presented. © 1969, ACM. All rights reserved.