for class on Thursday March 9, 2000
Please read the rest of section 5.2 of the Schneider and Gersting text (pp. 200-207). Section 5.3 on the history of computers is worth reading at some point, but subsection 5.3.4 is dubious, in your instructor's humble opinion. Be prepared to discuss the following:
Figure 5.18 shows the hardware organization of a computer whose instruction set is shown in Figure 5.19. A principal feature of Figure 5.18 is the single central bus, which allows communication between any two elements wired to it. Real computers, however, are not organized this way, mainly because this structure prevents much overlapping of operations. Real computers replace the single bus with a set of more specialized communication paths, many of which can be used simultaneously.
Try to come up with an alternative organization that only connects elements that need to be connected to perform the instructions of Figure 5.19. For example, the MAR register only needs to get its input from two possible places: the PC register (so that instructions can be fetched from memory) and the IR register (so that memory operands denoted by CON(X) in the table can be fetched). Make a sketch of your ideas. You will find multiplexors extremely useful--see, e.g., Figure 5.12.