you are an idiot. the effective bandwidth is what matters and it's irrelevant how it achieves that.
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BOTH of those would perform exactly the same if the same architecture and running at the same clock speeds. The fact that one uses 128-bit bus and the other uses 256-bit bus is 100% irrelevant if the effective memory bandwidth is the same and everything else is equal.
I just want to add, they will theoretically perform similar, but not necessarily exactly the same, it all depends on the GPU architecture. GPU memory controllers are currently structures as multiple 64-bit controllers, each can only communicate with one cluster/GPC at the time. Having fewer faster memory controllers would require faster scheduling to keep up, while having too many controllers will increase the risk of congestion on one of them. So it all comes down to a balancing act; how the clusters, memory controllers and the scheduler work together. Simply doing a major change on one of them without redesigning the others will create bottlenecks.
It might be wise to distinguish between theoretical specs and actual performance. Just look at:
Vega 64: 4096 cores, 10215 GFlop/s, 483.8 GB/s.
GTX 1080: 2560 cores, 8228 GFlop/s, 320.2 GB/s.
I wonder which one performs better…
Compared to:
GTX 1080 Ti: 3584 cores, 10609 GFlop/s, 484.3 GB/s.
As we all know, Vega 64 have resources comparable to GTX 1080 Ti, so it's not the lack of resources like many AMD fans claim, but the lack of proper resource management.
In conclusion, theoretical specs might be similar on paper, but their actual performance will depend on the complete design.
Again, this is all theoretical. If the same bandwidth is achieved by two cards, but one runs the memory at 100MHz while the other runs at 1,000MHz, the latter can a have a tenth of the former's latency (assuming that the data is already available to read on the next clock cycle - it usually isn't).
If I may add, memory latency is substantial, for DDR it's 50-60 ns for access, even more for GDDR. When you're talking of speeds of 1000 MHz and above, the latency factor becomes negligible, and higher clocks more or less just impacts the bandwidth.
AMD already said that there will be no gaming 7nm VEGA
So stop dreaming :-D
AMD have said all along that Vega 20 is targeting the "professional" market.
AMD can certainly change their mind, but as of this moment their position is still unchanged. But why would they bring Vega 20 to the consumer market? It only scales well with simple comute workloads, and Vega 20 is a GPU built for full fp64 support, which have no relevance for consumers.