Re:It also helped MS (Score 5, Informative)

For example in a console, you normally want all the RAM shared between GPU and CPU. There's no reason to have them have separate RAM modules. The Xbox 360 does this, there's 512MB of RAM that is usable in general. The PS3 doesn't, it had 256MB for each CPU and GPU. Reason is that's how nVidia GPUs work in PCs and that's where it came from. nVidia didn't have the time to make them a custom one for the console, as ATi did for Microsoft. This leads to situations where the PS3 runs out of memory for textures and the 360 doesn't. It also means that the Cell can't fiddle with video RAM directly. It's power could perhaps be better used if it could directly do operations at full speed on data in VRAM but it can't.

Being a (former) PS3 and 360 dev, I have to say this is not true. Let's start with the memory split. Both consoles have about 20GB/s of memory bandwidth per memory system. Only the PS3 has two of them, giving it twice the memory bandwidth. The 360 compensates for that by having EDRAM attached to the GPU, which removes the ROP's share from your bandwidth budget. Especially with a lot of overdraw, the bandwidth needed by the ROPs can get huge (20GB/s, anyone?), so this would be a nice solution where it not for two things: the limited EDRAM-size and the costs of resolving from EDRAM to DRAM.
The RSX can also read and write both to XDR (main memory) and DDR (VRAM), giving it access to all of memory. The reason it is tighter on texture memory is because the OS is heavier.

About access to VRAM, it is true that reading from VRAM is something you don't want the Cell to do. It's a 14MB/s bus, so it is of no practical use for texture data. Writing into VRAM is actually pretty ok, as it's at 5GB/s, which is more or less achievable without trouble. At 60fps that's more than 80MB per frame.

In general, both design teams made sound decisions. The 360 has a significant ease-of-use advantage to PC developers with DirectX experience. The PS3 on the other hand is a lot more to-the-metal, but allows for some pretty crazy stuff. Sadly, most development these days is cross-platform, so you won't see a lot Cell-specific solutions. It's just not cost-effective.