Abstract: Extending the size of the main memory of a data processing system having a synchronous inner storage unit by attaching a relocation translator having special connection interfaces and translated addressing for attaching a synchronous outer storage unit and an asynchronous storage unit which may be remotely located from the processor. A differnt form of storage cycle is generated by the translator for interfacing each of the three storage units being accessed. The translator performs address translation which expands the number of bits in the physical address to support the extended main memory. The extended address uses a concatenation of a program-derived address and a machine-derived address key.The maximum extendable size of the memory can substantially exceed the maximum addressing capability of any program, which is determined by the relocatable addressability obtained through any stack of segmentation registers.