462 EVOLUTION OF COMPUTER BUILDING BLOCKS
Figure 7. CAD system at CMU.
shows, the CMU-l 1 was implemented with significantly less components (IC packages) than either the PDP-l1/10 or the PDP-l 1/40, which are processors built with MSI components, and the performance of the CMU-l1 falls between these two MSI processors. However, the economy of implementation is not nearly as significant as was realized with the LSI-l1 although the CMU-l1 is able to perform at twice the speed of the LSI-11. The LSI-l1 is a processor implemented with NMOS LSI microcomputer packages in which the entire data path (with 8- bit data paths) was put in a single package and both the control and data packages for the LSI-11 have been specialized to efficiently emulate the PDP-l1 architecture.
Earlier we discussed improvements that are possible in the CMU-11 design and argued that a second iteration on the design could boost the performance to that of the PDP-l1/40 and could be implemented in about 95 rather than 144 packages. To achieve a more cost-effective design than this will require either the development of some LSI control circuits specific to the processor's instruction set or the specification of a new computer architecture tailored to make the most efficient use of the functions provided in the LSI circuits.