The overlay of information from the computer memory to a peripheral memory and its return to the computer memory are facilitated by a unique format for original and copy descriptors. The copy descriptors have a first field that designates either a base address or the location of its original, and a second field that designates an index. The original descriptors have a field that designates the base address. The copy descriptors are automatically generated from their originals. When a copy descriptor is retrieved, the first and second fields are added to form the absolute address if the first field is the base address. If the first field is an original descriptor location, the base address of the original descriptor and the index of the copy descriptor are added to form the absolute address. Upon overlay, the copy descriptors to be updated are sensed by comparing their base value with the base value of the array to be overlaid. They are updated by substituting the original descriptor location for the base address and the original descriptors are updated by substituting the peripheral memory address for the base address. Upon return of the overlaid information to the computer memory, only the original descriptor must be updated.