kaveri apu's & hybrid crossfire still unanswered questions

[semperaye]

My A10-7850k is paired with 8 gbs ddr3 2400mhz ram.

I understand that I can only crossfire up to an r7 250. The queston a lot of people are having is that since the r7 250 ram speed isnt even near 2133 (its in the 1k's), wouldn't it bottleneck the igpu that has access to 2133-2400mhz? If so then it may be better to not crossfire at all as the entire system would run at the GPU speed not the 2400mhz.

With that being said. Would the r7 250x that uses faster ddr5 (I think near 2500mhz) crossfire with the igpu at 2400mhz? Would the system run at 2400mhz since it is the lowest speed in this case, basicly forcing the dedicated GPU to run in ddr3 mode? Or would the igpu simply share the dedicated gpu's ram, allocating the 2400mhz ram for CPU purposes only thus limiting bandwidth to 2 gbs?

I really hope someone can answer this. No one has after asking hundreds of times on YouTube, and elsewhere. Thanx toms community!

 

[k1114]

Cf never runs at the lowest common denominator's speed (sli does). They are simply held back as they're rendering alternating frames and one would just wait for the other to render the frame. Vram speed is only one part of the equation and in the end it's performance that matters in which is held back. The gpu has a higher bandwidth even though the speed is lower because it's 128bit bus vs 64 for the cpu. Truthfully it's better to just get a higher end card and forget about dual graphics. But it was only intended for low budget builds, not really anything I'd call gaming worthy. But dual could still be better because 2 slightly slower gpu/igpu is still faster than either alone. It has more to do if the drivers and the game is optimized if dual even helps.

The 250 has a gddr5 version so no need to bring in a gpu that can't even dual. As gddr5 is 4x actual, it's effective is 4600 with a 1150 memory clock which would mean it's quite a bit faster than ddr3 for your cpu. The same still applies and dual could be better than either alone.