Question why do graphic cards require dedicated memory?

[in241]

Just a general question.

 

[IntelUser2000]

Two reasons:
-Graphics applications need much more memory bandwidth to perform well. System memory is much larger in capacity but the negative of that is it can't be as wide. It's a traditional trade-off between speed and capacity. Therefore, it has its own dedicated memory with much wider paths and thus higher bandwidth.
-Sharing a system innately results in worse performance. If it shares with system memory, there has to be some way of conflict resolution and its nowhere near ideal. In purpose built systems like consoles(in other words, not general purpose) not only the developers optimize the setup to minimize this loss but cost limitations justify having a shared system with all its constraints.

 

[Mopetar]

Technically they don't. APUs all use the same system memory for the CPU and GPU cores, but as the poster above has said the performance isn't nearly good enough unless you're using a really low end GPU.

 

[KentState]

GDDR vs DDR characteristics is the main reason. Both memories types are optimized for their respective processors so sharing would causing performance issues if saddled with one type over the other.

 

[Stuka87]

GDDR vs DDR characteristics is the main reason. Both memories types are optimized for their respective processors so sharing would causing performance issues if saddled with one type over the other.

GDDR is superior to DDR in almost every respect. The issue is that GDDR costs significantly more. Both the Sony and MS use only GDDR memory in their consoles in a shared system. There is nothing that would prevent using GGDR as s system memory if the CPU and Mobo both supported it. But people would be pretty unhappy with the cost associated with doing so. As both the mobo and memory sticks would be more expensive.

You want dedicated memory for a GPU because of the required bandwidth. The biggest hamstring for iGPU's is the limited bandwidth associated with using system memory.

 

[KentState]

GDDR is superior to DDR in almost every respect. The issue is that GDDR costs significantly more. Both the Sony and MS use only GDDR memory in their consoles in a shared system. There is nothing that would prevent using GGDR as s system memory if the CPU and Mobo both supported it. But people would be pretty unhappy with the cost associated with doing so. As both the mobo and memory sticks would be more expensive.

You want dedicated memory for a GPU because of the required bandwidth. The biggest hamstring for iGPU's is the limited bandwidth associated with using system memory.

It's not superior in every respect in regards to a PC and consoles don't mean much for this discussion as they have a completely different purpose. The bus width of GDDR makes it less optimal for general processing tasks. You would waste a bunch of bandwidth, moving around small amounts of data, which cpus typically handle. Just in the same way that the narrow bandwidth makes it less ideal for a GPU. The XB1 and PS4 can get away with a shared architecture as very little productivity work is being done in the same way that an integrated gpu is fine with shared system memory since it's not meant for gaming.