Whether CPU and GPU share ram is orthogonal to whether the gpu and cpu are on the same die. You can do any combination of same die same ram, different die same

Whether CPU and GPU share ram is orthogonal to whether the gpu and cpu are on the same die. You can do any combination of same die same ram, different die same ram, etc etc. The advantage of GPU having it's own memory is you can use super high throughput ram that the GPU needs, while using higher capacity/lower energy/cheaper ram for the cpu. The downside of using separate ram is that you have to shuttle data back and forth from one ram to the other quite a bit, as well you get less flexibility in how your total memory is used.