It seems there are 3 key things which distinguish the modern "unified memory architecture" from its predecessors:
1. Pointer passing instead of buffer copying
2. Separate bus for memory access alongside the PCIe bus
3. No partitioning of RAM into exclusive CPU vs. GPU areas
These features seem to have come at different times, and it's the combination of all three that defines the modern approach. Broadly speaking, whereas classic iGPUs were still functionally "peripheral devices", modern UMA/HSA iGPUs are coequal partners with their CPUs.
AMD seems to have delivered the first hardware meeting these criteria about 8-9 years ago, beating Apple to the punch by a couple years. However, AMD's memory bandwidth can be quite a bit behind Apple's. The M1 Pro handily beats anything AMD had out at the time (200 GB/s vs. 120 GB/s), and the M1 Max has double that bandwidth.
It seems there are 3 key things which distinguish the modern "unified memory architecture" from its predecessors:
These features seem to have come at different times, and it's the combination of all three that defines the modern approach. Broadly speaking, whereas classic iGPUs were still functionally "peripheral devices", modern UMA/HSA iGPUs are coequal partners with their CPUs.AMD seems to have delivered the first hardware meeting these criteria about 8-9 years ago, beating Apple to the punch by a couple years. However, AMD's memory bandwidth can be quite a bit behind Apple's. The M1 Pro handily beats anything AMD had out at the time (200 GB/s vs. 120 GB/s), and the M1 Max has double that bandwidth.