The instruction set of many computers permits referencing certain areas of main storage more efficiently than others. For example, "base-offset" addressing favors small offsets. This report discusses the problem of how to optimally assign data to storage on such a machine, subject to the restriction that the locations chosen are not to change with time. The emphasis is on truly optimal solutions, although many simplifying assumptions are made. Some of the results apply to the problem of optimally placing "read-only" files on auxiliary storage. Areas for further work are suggested. © 1978 Springer-Verlag.