Re: For the same reason you share it with the memory controller: On the net basis, you save power.
There's a difference, Joe. Integrating the memory controller is relatively "cheap" as far as silicon area and power. You can integrate the most high end DDR2-800 (or even higher rated controller) quite easily. Now, if we're talking about integrated graphics, there's a limit on the die size and power budget you can offer here. AMD can't work magic and put an R600 GPU into their CPU without rating the combined product at 200W TDP. Doing this would return back to the days when we had problems cooling the CPU and offering adequate power delivery.
The most likely product we'll see from Fusion is a combined CPU and GPU that has had to derate the performance of both in order to fit in the same power envelopes that current mainstream processors currently exist. For example, a 65W TDP Fusion processor might include 45W of CPU and 20W of GPU. A 95W TDP might include 65W of CPU and 30W of GPU. Essentially, they both have to share the resources available to them.
Of course, 30W given to a GPU on 45nm will result in some decent performance, and it will go well beyond what Intel could integrate in the chipset. So I see this being a good low end play, and also a way to get cheap graphics to mainstream buyers. And I wouldn't be surprised if the successor to Nahalem, called Gesher, has integrated graphics on the low end skus as well.
But as for the high end skus, you are better off leaving it out and letting your CPU take advantage of the full power budget. Most likely, people buying high end skus will also be buying discrete graphics cards, which will outperform Fusion by several fold, thanks to the vastly larger area and power budgets they have at their disposal.
There's also the question of whether a Fusion processor will also integrate GDDR, or if they will move both CPU and GPU pipelines through DDR. If the latter is the case, they will still be well behind discrete GPUs of the time. And if they do integrate GDDR, will it have to be in addition to the DDR? That means extra pins, extra power concerns, etc. Otherwise, moving completely to GDDR will mean that Fusion processors will need memory to be soldered onto the motherboard, since GDDR does not support DIMM sockets.
There's a lot of things to keep in mind here, but as I thought of it, I kept on being reminded of a low end play that also excels in mobile, but not something that will compete with high end microprocessors.
AI
