|
Fig. 5.7.1. shows schematically how the MBR and MAR are connected to the memory words. The MBR is always the same size as one cell of memory. If each cell is 8 bits wide, then the MBR is 8 bits. The MAR bears a more subtle relationship to memory. Since it holds the address of the cells, its bit width is log2n where n is the number of cells in the memory. Thus, if there were 1024 cells, numbered from 0 to 1023, the MAR would need to be 10 bits wide. Thus, the MAR and MBR are often of different sizes, and bear no relationship to each other. The number of cells in a memory is almost always a power of 2 because of this addressing mechanism. |
