Azul (and AFAIK most lisp machines) does not do garbage collection in hardware. In these contexts the "GC HW" involves hardware acceleration of read/write barriers required by concurrent and incremental GCs (which otherwise requires the compiler/JIT to inline implementation of barriers into user code). The reason why Azul can now use stock amd64 CPUs is that they found that you can abuse the MMU to provide exactly this kind of HW accelerated barriers.