Hey guys, I'm back!
***tumbleweed blows by***
Alright, I doubt any of you remember me, but I used to post a bit in the old Wii U speculation threads. I've been on a self-imposed exile from GAF for the past couple of months as I'm in my final year of college, but I've decided to make a brief return to cover a few things that I think need to be cleared up here in this thread.
There was a bit of discussion a few pages back on the console's CPU, and I thought it'd be worth spelling out what we know about the CPU, and what it means as far as the console's performance is concerned.
Wii U's CPU
The Wii U, by all accounts we've had thus far, has a tri-core IBM PowerPC CPU, with 2-way SMT (symmetric multi-threading), OoOE (out-of-order execution) and 3MB of L2 eDRAM cache. (The L1 cache, by the way, will be 32kB instruction cache + 32kB data cache, which is standard for all of IBM's PPC CPUs.) The CPU is expected to run somewhere north of 3Ghz (and I'd put 3.5Ghz as the absolute upper bound on that).
Given all this, the CPU would be expected to perform about the same in terms of raw computational power (flops) as the XBox360's CPU. The Wii U's CPU does have a couple of advantages, though, in terms of how efficiently that power is used.
A lot of modern CPU design isn't focussed so much on getting as many cores to run at as high clock-rates as possible (even in energy-guzzling server chips), but rather on getting the CPU to run as efficiently as possible, in particular minimizing the amount of wasted cycles. In old microprocessors, if the processor doesn't have the data it needs to perform an instruction, it has to wait until the data arrives from memory. Every clock cycle the data takes to arrive from memory is one in which the processor is doing nothing; it's a wasted cycle. If you're reading from memory a lot, these wasted cycles can add up to a considerable portion of the processor's time, and the actual performance you get will be a lot lower than the processor is in theory capable of.
There are two main technologies that modern processors use to minimize the proportion of cycles that are wasted. The first is the cache. This is a small pool of memory on the CPU that automatically pre-loads data as it's needed, and can then be accessed by the CPU at a much lower latency than main memory. The Wii U's CPU has a cache three times larger than the XBox360's CPU's, which means more data in low-latency range and hence fewer wasted cycles. It should also be expected that the cache in the Wii U is probably more advanced in it's implementation: ie. better at figuring out what data will be needed and when.
The second relevant technology is out-of-order execution. In a processor which is capable of out-of-order execution, instead of simply waiting when a piece of data isn't available for an instruction, the processor will go ahead and execute the next instruction along (if it can), or indeed the next instruction after that, or the next instruction after that, etc. This can, in some cases, substantially reduce the amount of wasted cycles, and it's a capability which the Wii U's CPU does have, and the XBox360's (and PS3's for that matter) doesn't have.
So what does this mean for games? Well, for some in-game CPU tasks, such as physics, the benefit will be pretty small. Physics is generally pretty linear code, so won't gain much from out-of-order execution or the bigger cache. By contrast, non-linear code like AI will benefit hugely from out-of-order execution and a large cache, so we'll see very significant improvements in AI performance on the Wii U's CPU compared to the XBox360's.
So, physics-heavy shooters like Red Faction wouldn't see much improvement CPU-wise on the Wii U, whereas AI-heavy games like RTSs should run significantly better. Most games will be somewhere in the middle, with a decent, if not amazing boost in performance over the XBox360's CPU. Keep in mind, though, that even if the CPU isn't any more efficient at running physics code, the fact that it's more efficient at other things means that developers have more power left to dedicate to physics, so all else being equal, we should still see better physics in Wii U games than XBox360 games in many cases.
It is worth noting, though, that even if the Wii U's CPU may be a bit disappointing to some, the HD consoles this generation (especially the PS3) went overboard with regard to their CPUs to the point where a lot of graphics work is offloaded to the CPU on many titles. A console with a modest boost in CPU power and a larger jump in GPU capabilities would make for a much more balanced machine.