How important is system bandwidth

[TXSPheonix]

Originally Posted by jacksmith28

WOW. 94 posts! put this thread to rest...

WHY????

I can't wait till Shaun posts the link...

[shaun]

Article's done, going through editing. End of the week or sooner.

Edit: he's waiting on some details on RSX.

Anyone has any info on RSX email me shaun[at]pixelefx[dot]com or post it here or on our forums. ty.

[shaun]

lol. i got owned. $599 it is. i stand corrected.

[pApA SmerF01]

Originally Posted by shaun

lol. i got owned. $599 it is. i stand corrected.

i think we all got a little owned shaun...it's ok...

but seriously, did your friend ever get done with that article?

[shaun]

No. We got a little sidetracked with Oblivion. That and not much has been published about RSX yet.

I'll see what I can dig up for you guys though.

[pApA SmerF01]

Originally Posted by shaun

No. We got a little sidetracked with Oblivion. That and not much has been published about RSX yet.

I'll see what I can dig up for you guys though.

and if you find jimmy hoffa's corpse while looking, please inform me...i've had a bet running on that one for a while now...

[EbonySeraphim]

I seriously signed up for this forum after trying to do research on an Xbox360 feature and ran into this thread through a Google search. After reading it, and the posts that followed immediately afterwards, it almost makes me want to throw up. It's pretty sad to see such a horrible post claim to have any technical merit, when the post so clearly took everything IGN fed him through the Microsoft based assessment. I have skimmed over some of the dialouge and it seems Shaun is the only one with at least a vauge idea of the irrelevant context of Microsoft's bandwidth assessment.

I implore you guys to go out, and do research for yourself, and figure out what each of the bandwidth numbers means. Also look at the diagrams of each of the console's hardware to get a better picture of where things will have to flow through. When you do your own research, assuming you go deep enough and actually understand what you are being told, you will find:

1) The eDRAM bandwidth on the Xenos doesn't factor into the whole system. If the CPU needed to process graphics on the framebuffer, moving data out of the eDRAM to the CPU would be capped at 10.8GB/s(21.6GB/s both directions), which is the bandwidth between the Xenos and Xenon(CPU). Even if the GPU needed to do pixel shader work out of there, it would be capped at 32GB/s bandwidth which is the link between the parent and daughter dies.
2) The XBox360 CPU shares bandwidth with the GPU. The 22.4GB/s is the only link to the GDDR3 RAM, and if both the CPU and GPU are using it at the same time, the bandwidth is split.

--At this point, you should be wondering why Microsoft added those bandwidth numbers together to come up with a "total system bandwidth" which doesn't make any general sense. Their assessment of why bandwidth is important is true. But looking at their individual component needs and what will actually occur in games processing, their total system bandwidth makes no sense.

3) CPU RAM access is more latency bound than bandwidth in certain applications (especially general purpose). GDDR3 is RAM designed for graphics chips which offers higher bandwidth at the cost of high latency. I'm sure you may find some old articles which still claim GDDR3 is low latency, but compare it to XDR's latency and figure out which one is more approriate for a CPU to be using.

I'll stop here since I am already in the middle of a huge post for another forum (PS3Forums.com if you're interested). Am I a fanboy? Perhaps I am. Am I also a computer science major, with a hobby in game development and understanding of computer hardware? Yeah, I am that too. You don't have to believe me, but you should do research for yourself as academia, combined with unbiased reports from IBM and other sources, will allow you to arrive at a real comparison between the consoles.

[Enola Bomber]

And the gloves are off.... nice rebuttle.

[RSFlux]

Wow, you're a little late on the pickup Ebony...this thread has been dead for a long time.

Anyways, you're also talking a lot of hot air. Your post is well phrased and organized, but it's just wrong on a lot of points. First, you cite the speed that the CPU would be able to access the frame buffer as a bottleneck in the system. Anyone that has done even the slightest bit of graphics programming knows that you never need to access the framebuffer from the CPU. Yes, you can, but you just don't do it. All graphics cards work this way; this is not a "flaw" in the 360's design.

Next, you mention that the GPU/eDRAM link is 22.4 GB/s. While this is true, you fail to mention that for certain common processes such as FSAA, you have a 256 GB/s link. This does not speed up the pixel shader output in itself, but it removes the need to waste some of that bandwidth with processes such as FSAA which has historically taken a moderate chunk of processing time.

Last, you mention the latency of the GDDR3 RAM. The difference between GDDR3 and XDR is really negligable for the most part. This latency difference would only not affect most gaming scenarios, and where it does good caching more than makes up for this. Which brings me to my second point: Doesn't this bode worse for the PS3 than the 360? You say that this minor latency delta is a disadvantage, but the Cell SPEs have no local cache or branch prediction, which translates to a huge latency difference.

I applaud your efforts to add something to this conversation, but most of the bases have been covered by previous posts. And it is also apparent that you do not have any experience in the gaming industry since you are approaching this issue from a solely analytic viewpoint...you are not taking into account what actually matters to game programmers.

[SB100]

ride on brother , thats how 360 rolls