Apparatus for deriving addresses of data using displacements from base addresses which change only on call and return

In the digital computer system of the present invention, data items called immediate names represent other data items. The immediate name specifies either the address of the represented data item or the address of a pointer to the represented data item. Each immediate name contains a base address specifier specifying one of a set of architectural base addresses, an indirection specifier specifying whether the immediate name specifies the address of the represented item or the address of a pointer to the item, and a displacement from the specified architectural base address. The architectural base addresses are contained in registers accessible to a processor in the digital data processing system. The registers are loaded only when the processor preforms a call operation or a return operation. When the immediate name specifies the address of the represented item, the processor produces the address by combining the displacement specified in the displacement specifier with the architectural base address indicated by the base address specifier. When the immediate name specifies the address of a pointer to the represented item, the processor combines the specified displacement with the specified base address to obtain the address of the pointer, fetches the pointer into memory, and produces the address of the represented item from the pointer.