"Unified memory" has been around forever in one form or another, as it's simply a single address space (and physical location) for various independent subsystems. In graphics, it's probably been used since Amiga. (?) This is common in console GPUs which always punched above their weight. The ubiquitous Intel shared memory has been around for ages, although it was not entirely unified (reserved area for GPU, which it cannot escape; zero-copy still possible by allocating inside it and addressing data on CPU).