Um.... the whole system has 512 mgb's of ram which the whole system has access to due to a unified memory architecture. This means the CPU and GPU share the ram. So if the CPU is using 128... the GPU can use 384. This has it's pluses and minuses.
The PS3 however has 256 megs dedicated to the GPU and 256 dedicated to the CPU.
Both have their different faults and positives.
The PS3 however has 256 megs dedicated to the GPU and 256 dedicated to the CPU.
Both have their different faults and positives.