Will Sony (PS4) Fanboys be Questioned Xbox Engineers Allegations?

Digital Foundry vs. the Xbox One architects Now Xbox team for the second times has officially revealed all the papers and replied to those allegations (rumors) stating that PS4 is 50% more powerful over its Xbox One counterpart.

Do you think PS4 team will keep quiet about Xbox team allegations? Unless it's true.

"it would be great if someone with engineering background explain this to us"

Here are some of the Xbox engineers allegations (explanations):

1. There are two major areas of controversy surrounding the Xbox One design - specifically the areas in which it is considered weaker than the PlayStation 4: the memory set-up and the amount of GPU power on tap. Both systems have 8GB of RAM, but Sony chose 8GB of wide, fast GDDR5 with 176MB/s of peak throughput while Microsoft opted for DDR3, with a maximum rated bandwidth of just 68GB/s - clearly significantly lower. However, this is supplemented by on-chip ESRAM, which tops out at 204GB/s. In theory then, while marshalling and dividing resources between the two memory pools will be a factor, Xbox One clearly has its own approach for ensuring adequate bandwidth across the system.

Having ESRAM costs very little power and has the opportunity to give you very high bandwidth.

2. The combined system bandwidth controversy:

The controversy surrounding ESRAM has taken the design team very much by surprise. The notion that Xbox One is difficult to work with is perhaps quite hard to swallow for the same team that produced Xbox 360 - by far and away the easier console to develop for, especially so in the early years of the current console generation.

"This controversy is rather surprising to me, especially when you view as ESRAM as the evolution of eDRAM from the Xbox 360. No-one questions on the Xbox 360 whether we can get the eDRAM bandwidth concurrent with the bandwidth coming out of system memory. In fact, the system design required it," explains Andrew Goosen.

3.How ESRAM bandwidth doubled in production hardware:

There are four 8MB lanes, but it's not a contiguous 8MB chunk of memory within each of those lanes. Each lane, that 8MB is broken down into eight modules. This should address whether you can really have read and write bandwidth in memory simultaneously," says Baker.

"Yes you can - there are actually a lot more individual blocks that comprise the whole ESRAM so you can talk to those in parallel. Of course if you're hitting the same area over and over and over again, you don't get to spread out your bandwidth and so that's one of the reasons why in real testing you get 140-150GB/s rather than the peak 204GB/s... it's not just four chunks of 8MB memory. It's a lot more complicated than that and depending on how the pattern you get to use those simultaneously. That's what lets you do read and writes simultaneously. You do get to add the read and write bandwidth as well adding the read and write bandwidth on to the main memory.

4. Tweaking Xbox One balance and performance:

Every one of the Xbox One dev kits actually has 14 CUs on the silicon. Two of those CUs are reserved for redundancy in manufacturing, but we could go and do the experiment - if we were actually at 14 CUs what kind of performance benefit would we get versus 12? And if we raised the GPU clock what sort of performance advantage would we get? And we actually saw on the launch titles - we looked at a lot of titles in a lot of depth - we found that going to 14 CUs wasn't as effective as the 6.6 per cent clock upgrade that we did."

Assuming level scaling of compute power with the addition of two extra CUs, the maths may not sound right here, but as our recent analysis - not to mention PC benchmarks - reveals, AMD compute units don't scale in a linear fashion. There's a law of diminishing returns

Right. By fixing the clock, not only do we increase our ALU performance, we also increase our vertex rate, we increase our pixel rate and ironically increase our ESRAM bandwidth," continues Goosen.

"But we also increase the performance in areas surrounding bottlenecks like the drawcalls flowing through the pipeline, the performance of reading GPRs out of the GPR pool, etc. GPUs are giantly complex. There's gazillions of areas in the pipeline that can be your bottleneck in addition to just ALU and fetch performance."

5. GPU Compute and the importance of the CPU:

Interestingly, the biggest source of your frame-rate drops actually comes from the CPU, not the GPU," Goosen reveals. "Adding the margin on the CPU... we actually had titles that were losing frames largely because they were CPU-bound in terms of their core threads. In providing what looks like a very little boost, it's actually a very significant win for us in making sure that we get the steady frame-rates on our console."

This in part explains why several of the custom hardware blocks - the Data Move Engines - are geared towards freeing up CPU time. Profiling revealed that this was a genuine issue, which has been balanced with a combination of the clock speed boost and fixed function silicon - the additional processors built in to the Xbox One processor.

"We've got a lot of CPU offload going on. We've got the SHAPE, the more efficient command processor relative to the standard design, we've got the clock boost - it's in large part actually to ensure that we've got the headroom for the frame-rates," Goosen continues - but it seems that the systems's Data Move Engines can help the GPU too.