Bus width is orthogonal to the bitness of a CPU. QPI, the bus Intel CPUs use, is a 20 bit bus. HT, the equivalent AMD technology, uses a 32 bit bus, even on 64

Bus width is orthogonal to the bitness of a CPU. QPI, the bus Intel CPUs use, is a 20 bit bus. HT, the equivalent AMD technology, uses a 32 bit bus, even on 64 bit CPUs. HBM2, used on certain AMD video cards, uses a 1024 bit bus. The Commodore 64 had 8 bit registers, an 8 bit data bus, and a 16 bit address bus. We do not need 128 bit data types in hardware. We barely even need data types with 64 bits of precision. It crops up every now and then- for instance, 32 bit floats cannot store a latitude/longitude value precisely enough, however a 32 bit integer can store a longitude value to about 1 foot of precision if -2^32 is 180 degrees west and 2^32 is 180 degrees east. (this has the nifty benefit of 2s complement integer overflow doing the right thing, although only with longitude, not latitude. but I digress.) There are a handful of situations where you do need more precision than that- RSA and DH come to mind. But in those situations, you'll need arbitrary precision arithmetic anyway. A 128 bit register won't help a whole lot- certainly not enough to offset the cost of doubling the size of all your ALUs, even if the machine is a special purpose one that does nothing but sign SSL certs all day.