PlayStation 4′s 8GB of GDDR5 RAM shared between GPU is an advantage, rather than not explains K^2.
GDDR5 is used in graphics cards because it’s faster. If a high end GPU used DDR3 now, it would be crippled. The PS4 has 8GB of GDDR5 which is impressive and shared with the GPU.
Sharing isn’t a problem for an architecture like this. It’s an advantage. It’s not the same thing with PS2/XBox era RAM sharing, where CPU and GPU got access to a fraction of memory.
These 8GB are completely accessible by both processors. That means that everything that requires traffic between RAM and VRAM on PC and duplicates of various resources no longer needs any of that on PS4.
For example, consider streaming a texture on PC. First, the VRAM memory is “unlocked”, which means a duplicate storage space is created in RAM.
Then the texture data is read from HDD and copied over to RAM. Then the texutre is “locked,” which involves copying contents of texture in RAM over to VRAM via the PCIe bus. This is the biggest bottleneck on PC. On PS4 it is completely eliminated. Data is streamed from HDD or disk directly into shared memory.
Or say you want destructible environment in a PC game. You can either run physics on CPU, which isn’t terribly fast, and then you have to update geometry buffers in graphics memory. Or you can run all of the physics in GPU, altering geometry directly there, but then you have to pull it out into RAM so that your path finding and AI can use it.
Either way, you end up managing geometry both in VRAM and in RAM. Updating both copies constantly via the same PCIe bus. Again, a major bottleneck.
On PS4, you have just one copy of geometry sitting in lightning fast GDDR5 memory and both GPU and CPU have access to it. So either processor can be running physics, depending on which is more convenient, with GPU running graphics and CPU running AI all from the same geometry.
Some people said that the CPU cores are likely based on AMD’s Jaguar ones which aren’t that great and are clocked at a slow 1.6-1.8GHz. Time will tell if how good it is.
Still, the main point here is that CPU really doesn’t have to be all that great. PS4′s CPU is just there to run logic. AMD’s architecture isn’t the best even for that, but it’s definitely good enough. The entire edge of PS4 comes from the fact that both chips are sitting on the same die and are sharing memory. And whatever else you might say about AMD, they have most experience with this sort of design.
With Unreal engine and Havok already shifting their physics to GPU on the PS4 architecture, we will see some quite amazing stuff on PS4.
It will be quite competitive with PC market for the following two years, at least, and we wouldn’t be surprised if we don’t see some paradigm shifts in PC market because of this.
If somebody doesn’t end up manufacturing motherboards with GPU sockets and support for faster RAM, some people will be a little disappointed in the PC market.
