I don't think that's realistic; registers and SRAM are a lot more expensive than DRAM and consume a lot more power. I think having some combination of fast, ex

I don't think that's realistic; registers and SRAM are a lot more expensive than DRAM and consume a lot more power. I think having some combination of fast, expensive RAM and slow, cheap RAM in any system larger than a tiny microcontroller is just a fact of life. A different way to attack this problem is to make timing attacks harder by disallowing programs from reading the current time or inferring the passage of time by monitoring non-deterministic interactions between threads. Pure Haskell code (i.e. code that runs outside the IO monad) is an example of an execution environment that conceals timing from the running code. There are certain kinds of problems that aren't amenable to running in a completely side-effect and non-determinism free sandbox, but maybe for some applications it's a viable solution.