Other than memory size limits of 4GB, what is the penalty for running 32 bit applications on an OS running in 64 bit? For example. does a 32 bit application require that it's address space be allocated within the first 4 GB or does the OS and processor abstract this away from the application?
There has been a lot of push for 64 bit applications in the software community where I don't always foresee the applications requiring such a large amount of memory (e.g, Firefox), so I'm just curious of the benefits and pitfalls of running 32 bit applications on a 64 bit platform.