I need some verification on a topic involving Xbox 360.

[MarsVolta81]

While comparing specs...Microsoft says this:

"The Xbox 360 has 22.4 GB/s of GDDR3 bandwidth and a 256 GB/s of EDRAM bandwidth for a total of 278.4 GB/s total system bandwidth."

My question is on the EDRAM...is that supposed to be at peak for sequential access? and in a console setting will it even be necessary to access RAM like that?

 

[Goi]

As AT's latest XBOX article has pointed out, the 256MB/s EDRAM bandwidth quoted isn't the bandwidth from the GPU core to the EDRAM, but rather bandwidth from the EDRAM to the on-die floating point units. The main GPU core, which sits in a separate but connected die, has a "wide" bus running at 2GHz to the EDRAM. I expect it to be a 512-1024bit bus, therefore yielding a GPU-EDRAM bandwidth of 64-128MB/s.

 

[MarsVolta81]

That said. Would it be fair to say it's more or less efficient than PS3 at 22.4 GB/s of GDDR3 bandwidth and 25.6 GB/s of RDRAM bandwidth for a total system bandwidth of 48 GB/s.

 

[Goi]

Bandwidth wise, yes. However, remember that the EDRAM is only a sort of cache. I'm not sure if they actually address it as part of the main memory or does it act as a cache, but 10MB isn't going to be enough for. In fact, at high resolutions and with FSAA/AF, it won't even be enough for a single frame, so they're not always going to get that bandwidth. They're going to be accessing their main memory pretty frequently, which in their case is also 22.4GB/s.

Also, you can't just add up the individual bandwidths for a "total system bandwidth". It's kinda misleading.