>You can't use conventional 32-bit x86 code, so there seems little or no >benefit in allowing 32 and 64-bit code to be mixed.
Why not? Switching between 32- and 64-bit modes doesn't involve anything (apart from knowing the proper selector register values) that cannot be done purely in user mode. Specifically, I once successfully tried executing 64-bit code in a 32-bit process. Jan
