GPUs are going above DMA, DMA still needs memcopy and or address space translations which adds latency slows things down, with unified memory in theory you have

GPUs are going above DMA, DMA still needs memcopy and or address space translations which adds latency slows things down, with unified memory in theory you have a single address space and cache coherency across everything which means you can operate at the maximum bandwidth of all interfaces without wasting any cycles.