Realizing a Large Memory Space on a Microprocessor System
Elmer Frederick Pflug · Defense Technical Information Center (DTIC) · 1980
The memory space of current microprocessors is limited by the number of address bits inherent in the architecture. Several applications of microprocessors require large addressing space, for example, in multiple microprocesor systems with a single shared memory. This research is focused on obtaining cost-effective ways to achieve a large addressing space. Several different ways are suggested for this purpose. Applicability of these results to three real microprocessors is discussed. The microprocessors discussed are Intel 8080 Zilog Z80 and Motorola 6800. It is concluded that Intel 8080 and Z80 can address a large memory space with very little additional hardware, while Motorola 6800 requires much more hardware. A large memory is usually implemented as two-level hierarchy for reasons of cost-effectiveness. This research also focusses on the ways to organize a two-level virtual memory system for microprocessors. It is concluded that current microprocessors require a large amount of external hardware to support a virtual memory system. Even with this additional hardware, the virtual memory system is not as general as in large computer systems. The restrictions imposed on the system to correctly support a virtual memory system on a microprocessor are also discussed. (Author)