Abstract: Storage hierarchy comprising a main store with user and program data (L), a control store with micro code (C), and a processor buffer store which is commonly used for both data types (L & C). With no restrictions imposed, allocation of buffer space for L and C type data is self-adapting, since the address and replacement array are used jointly for both types of data.Alternatively, to reserve at least a minimum amount of buffer space for L and C type blocks, respectively, one or two space limit values may be defined and adhered to each time buffer block space is allocated anew. Thus the buffer space may be shared by the two types of data either in a fully overlapping (no space limit values), in a partly overlapping (two space limit values) or in a non-overlapping manner (one space limit value).