You need lightning fast GDDR and a massively fast pci-e bus to feed it due to the massive overhead of transferring data between the system ram and the gpu memory. HSA/HUMA removes that need so even if your memory is fairly slow in comparison, it doesn't matter as it won't need to do anywhere near as many operations.
Mantle is a totally different technology...
I think you're confused.. HSA won't fabricate anymore GPU power.. With regard to ram speeds think about it, if what you're saying is true. Why would the industry be moving onto DDR4 if all we need is HSA? It'll still be faster running DDR5 / DDR4 VS DDR3 in the exact same HSA based system.
HSA allows CPU/GPU a streamlining way of processing data, think of it more as a more efficient way of processing, it would use less power than the current way of doing the same given task, but not provide more GPU power...
So an HSA based setup with the right software could run programs with a lower power envelope.
Mantle isn't technology as such, i.e it's not the hardware itself, it's an API for lower level assess to the hardware. In that respect Mantle can subtract more performance from hardware than other API's...
This is where the whole picture comes clear..
HSA provides more efficient processing, lower power envelopes.
Mantle provides more performance from graphics hardware by getting lower level asses to GPU.
By utilizing both HSA and Mantle, AMD's future APU's have a real chance of offering an all in one solution..
