Exhaustive Performance Anaylasis of ATI 4800 platform

[Truckchase!]

In this post I'll examine the potential for a memory bottleneck on the 4800 series. As I stated earlier:

here's a different take on how to tell what impact mem bandwidth is having...

1> benchmark 4850 @ stock speeds
2> oc the GPU and vMem by a static percentage (15&#37 and bench
3> OC just the GPU and Just the vMem by the same static percentage and benchmark each oc seperately.

Compare the results to see how large of an impact the vMem overclocking has on performance vs. the gpu. In all actuality, you need only to do step 1 and 3, but 2 is always fun to compare against to make sure there isn't an odd unknown variable.

Here's an example from when I did this on a 2900xt:
http://www.xtremesystems.org/forums/...5&postcount=31

I've done this at 1600x1200 with AA on/of and Aniso on/off. Here are the results from the two extremes on a 4850:

Note that the 4850 is the more effective card of the two to check for memory bandwidth bottlenecks in this fashion because of the significantly lower overall bandwidth. That being said, I'll still test the 4870 later.

Quick note on the graphs... stock speeds are 100%, this shows the performance relative to that for ONLY gpu overclocked and ONLY mem overclocked. All overclocking for this test was by 12%.

This platform definitely looks to be more bandwidth restricted than the 2900, which is no surprise being that the 2900 had a full 512bit interface. I unfortunately don't have 3870 numbers to compare to, but I suspect that the results would be similar to that of the 2900 since the overall performance characteristics are very close. There is certainly potential justification here for GDDR5, as the bottlenecks on some games are close to being evenly split across the memory and gpu.

More analysis to come on these numbers...