AMD built "Heterogeneous System Architecture" for their APUs to do the same thing, but since their APUs all ended up mostly targeting cheap/low-power/low-profile laptops and business machines, it was never actually utilized (from what I've been able to find, there's no public API to actually use this as designed and you still have to copy things from "system RAM" to "GPU RAM" even though the hardware was designed to support zero-copy, whereas Apple has made it all automatic when you use Metal)