< Address bus should be as wide as you think you might need plus a bit mor < As Allison said (again! Why oh why did I delete her post?) you want you < processor to be able to think about huge memories even if you can't buil < them and have to swap to disk. Actually the addres bus can be smaller than register size. For example we could build an 80 bit machine with 60bit address busses. The 60 bits is more than enough to address most likely memory needs for a long while yet if you need to do address math or other math 80bit long registers may make it much easier. The datapath bus can be any size as well but larger is generally better. The assumption of symetry is likely the most false. Allison