What if?

[Paul Berger (Canada)]

(05-17-2016 11:28 PM)Joseph_21sv Wrote:  Paul, how wide an address bus do you mean, as wide or twice as wide as each individual CPU? If twice as wide, I would not expect that the two CPUs would ever need to contend address bus access because each individual CPU would then have exclusive access to an individual slice of the address bus, thus obviating the need for either option.

Ok lets take a hypothetical new system board that has a 32 bit data bus and a 32 bit address bus. 32 bits of address will allow you to access about 4.29E9 memory locations. If as you propose we split both the address and data bus between the two processors, so each processor has 16 bits data and 16 bits address, well 16 bits of address only allows you to access 65.5E3 memory location, yes it would work but that would hardly be adequate for a modern system. Not only that but since this system board is designed for 32 bits of data and 32 bits of address the memory array is going to be laid out as an array of 4.29E9 32 bit words. The word in that is addressed in that array that is being accessed will be the one pointed to by the sum of the bits active on the whole 32 bit address bus, so with what you propose you would have two separate processors providing half of that address word, the result to say the least would be chaotic. For this to work as you propose with a split address and data bus, the memory array would need to be designed so that it could be reconfigured to split the memory into two separate 64K word array, and if someone was designing a system board for a 32 bit processor with a 32 bit address bus, why would they do such a thing?