actually what shinen mentioned is that 16MB of edram on wii u is enough for 1080p with double buffering
Manfred Linzner of Shin’en:
‘Wii U eDRAM usage is comparable to the eDRAM in the XBOX360, but on Wii U you have enough eDRAM to use it for 1080p rendering.[/size]
In comparison, on XBOX360 you usually had to render in sub 720p resolutions or in mutliple passes.[/size]
Even if you don’t use MSAA[/size] (MultiSample Anti-Aliasing) [/size]you[/size] already need around 16Mb just for a 1080p framebuffer (with double buffering). You simply don’t have that with XBOX360 eDRAM. As far as I know Microsoft corrected that issue and put also 32MB of Fast Ram into their new console.[/size]
We use the eDRAM in the Wii U for the actual framebuffers, intermediate framebuffer captures, as a fast scratch memory for some CPU intense work and for other GPU memory writes.[/size]
Using eDRAM properly is a simple way to get extra performance without any other optimizations.[/size]
the xbox 360 edram+ROPS and other components had an internal bandwidth of 256GB/s, the bridge between the gpu and the edram was limited at 32GB/s
So obviously the wii u edram has more than 256GB/s otherwise the porting wouldnt be so easy, right now speculation goes for 563.2GB/s or more, not to mention that if xbox 360 10MB was barely enough for the 720p with double buffering and wii u 7.1MB of edram is enough to hold 720p with double buffering then clearly the wii u edram must pack much more bandwidth
The picture you posted blatantly shows you are wrong. In fact, its in the last part of the text you quoted.
The 360 did not have 256Gb of bandwidth to the edram, the edram had 256Gb of bandwidth to itself, and the rops, on the daughter die, across a bridge, from the rest of the system, if anything else wanted access to that edram, it had to cross the bridge at 32Gb/s for the request, and back again, waiting on the added latency of crossing the bridge to the daughter die. The 360's edram didnt have enough capacity, so it had send the framebuffer in over chunks, the latency was horrible, and the bandwidth sucked because there was a 32Gb a second bridge between the edram and the system.
Its not bandwidth that makes the wii u's edram smoke the 360's, its the fact it has 3x the capacity, is within immediate access of the entire system instead of gated off on a duaghter die, and so it had none of the latency.
There are 3 factors that affect the performance of ram, you want all three to be as high performing as possible, but realistically, you usually can only get to choose two that will be high performing, bandwidth is just one of them. Capacity and Latency are just as important, and depending on the situation, can be far more important than bandwidth.
Shinen uses that Wii u edram to store 3 720p framebuffers for fast racing neo (And thats only using half of it, and already over the 360's capacity a time and a half). The 360 couldnt dream of doing that even if its bandwidth on that edram and rops was 500 Petabytes. It doesnt the capacity, and it has too much latency.