How PS4 Could Overpower a More Powerful PC
Some have criticized Sony for abandoning the exotic, custom processors they have usually used in their PlayStation consoles for more standardized "off the shelf" PC parts. They have drawn up comparisons with how much money it would take to buy an equally powerful PC and how capable that PC, and therefore assuming PS4, is using benchmark software. These comparisons are not valid, and this is not a disadvantage for Sony. I'll explain why.
While PS4 uses a customized 8 core version of AMD's "Jaguar" CPU, and a GCN compatible Radeon GPU, there are some fundamental differences between this hardware and an off the shelf PC. First, as many sites have stated before, PS4 will not be burdened by operating system overhead or restrictive API's like a PC is. In addition, the components in PS4 are manufactured with high bandwidth in mind. Much higher than PC. PS3's 8GB's of GDDR5 ram is typically only used in PC GPUs, and in much lower quantities. The PC GPUs have their own dedicated pool of GDDR5, while the CPU has it's pool of system RAM that is usually a good bit slower.
PlayStation 4's RAM setup is 8GB of unified GDDR 5. There is no faster RAM pool and slower RAM pool. There are no walls separating the GPU from accessing every available MB of the CPU's RAM, or the other way around as well. While this does mean that both the CPU and GPU accessing the same pool of RAM at the same time would reduce overall bandwidth for each device, the PS4's architecture actually allows for some ways around that, as NeoGAF user .nimrod points out:
You are underestimating the importance of shared memory and an on-die GPU. These features allow for modifying and using data on both processors without a readback from VRAM, which is a very expensive operation on PC GPUs that can cause pipeline stalls. For example, modern engines like Frostbite 2 even implement a software renderer for occlusion culling, rasterizing occlusion volumes on the CPU just to avoid a readback operation. You wouldn't need that on an architecture like the PS4. Shared memory would also allow things like generating geometry on the GPU, doing collision detection on the CPU and rasterizing on the GPU again without any readbacks or copying of memory. You just cannot build a PC with those features yet, no matter how much money you are willing to spend.
When you have an operating system designed to run quietly in the background and consume as little CPU and RAM as possible, much faster and unified RAM than PC, the ability to milk every last drop of power out of every component because you do not have to make your software compatible across a wide range of CPUs and GPUs, and the ability for your CPU and GPU to both assist each other with render operations and computing without taking a bandwidth hit, you end up having to buy a PC that would be considerably more expensive than a PS4 will likely be in order to get the same level of performance. There is no doubt that you could spend a small fortune and assemble a PC that would have the hardware capabilities to blow PS4 out of the water, even with these limitations. However, when it comes to bang for your buck, PS4 does easily provide a better hardware value for gaming than an equally priced PC would.