There are actually two different sides to this question. When people refer to "64-bit" CPUs, generally they're referring to the address space. 64 bits of addre

There are actually two different sides to this question. When people refer to "64-bit" CPUs, generally they're referring to the address space. 64 bits of address space increased the addressable memory by a factor of 2^32 over 32 bit processors. That's a vast increase, and we're nowhere near exhausting it. Even current supercomputers are massively parallel, so individual nodes typically only have a few GB of memory. The largest memory server that I'm aware of uses up to 4 terabytes of memory, so that's a factor of 1024 beyond 32 bit addressing, or 42 bits. That leaves 22 bits of expansion, each one doubling the capacity of the last. I expect that won't be exceeded before 2100 at a minimum. On the other hand, there's the size of the general-purpose and other registers. That's currently 64 bits also in AMD64 processors (including Intel's). There are, however, specialized vector instructions that currently operate on 256 bits at a time (AVX) and the next generation due in 2015 will operate on 512 bits at a time (AVX-2). So, on address space the answer is "not anytime soon". On the processing side, the answer is "we're already beyond 128 bits". :-)