I'm wondering how GPU memory works on the iPhone and iPad. After reading the Apple tech specs on the iPad 3 (http://www.apple.com/ipad/specs/) it says the A5X is a system on a chip with a dual core CPU and quad core GPU. Do they share the same system RAM? How does the GPU do fast operations if it has to work in system RAM? I'm sure it's my lack of understanding of the system on a chip architecture that is confusing me, but if someone can chime in with their knowledge that would be helpful.
iPhones/iPod Touches/iPads all have a Unified Memory Architecture which mean that both the CPU and GPU share system memory. There is no dedicated video memory on these devices.
The advantage is that you don't need to worry about running out of video memory for your textures or vertex data (your app will be terminated by iOS for using too much memory before that happens). The disadvantage is that you share the same memory bandwidth for gameplay and graphics. The more memory bandwidth you dedicate to graphics, the less you will have for gameplay and physics
On the newer processors such as the A5X, A6 and A6X Apple has doubled the bandwidth to memory for the GPU to 128bit whereas the CPU still has 64 bit access.