64 bit JIT and 32 bit JIT are 2 very different beasts which is what one would suspect. But still I was rather surprised that 64 bit JIT was able to reduce the call stack of a call by 20% in comparison with 32 bit JIT. A piece of my code crawls the call stack to gather some runtime characteristics and it broke on a 64 bit machine. That's how I started a small investigation and found this difference. In most cases it's not a good idea to rely on the way JIT works as this is subject to change but from time to time there is simply no other way. If you look for more information about 32/64 JIT you can check this blog post of Scott Hanselman which is an overview with links to other Microsoft bloggers that dive much deeper into details.