GPU socket on mobo?

[vidiot5533]

This is a theoretical scenario that I don't expect to work, but had floating in my head for a few days.

 

TL;DR up front, why is the cpu motherboard mounted, and the gpu pci-e pcb mounted?

 

Since integrated graphics and dual socket motherboards exist, what is the prospect of having a GPU socket on a motherboard? It stands to reason that it would give the user the ability to choose how much GDDR memory to install (within reason) and which chip to have. It would also place the graphics closer and be more comparable to integrated graphics 

 

Is it a motherboard real estate issue that would prevent top tier performance? Backwards compatibility? Die size changes? Other? All the above? It would be interesting to see the design process and see why engineers have decided against it/not considered it. 

 

And for that matter, if a graphics card is best suited to not be on the motherboard, wouldn't a cpu be better on a card too? What makes it better on the motherboard despite the processor being better on a second pcb? I would thing a cpu/ram pcb connecting to the mobo would greatly improve interoperability between generations with a good communication protocol. This would also put both high-temp devices in the same orientation which could increase cooling capability. although I'm no expert, that's all just conjecture.

[WhitetailAni]

During the Pentium II/III days, there was a the Slot 1 "slocket". You had your Pentium 2/3 chip on a card, and put that in the motherboard.

(I think) Intel did this to make the cache closer to the processor, as it wasn't integrated into the processor; instead it was on the motherboard.

Also, it used to be that almost everything was on a card - drive controllers, parallel/serial ports, sound, floppy controllers, modems, etc.

[Grabhanem]

I'd guess the main problem would be memory bandwidth. GPUs require an absurd amount of memory bandwidth in order to function efficiently, and running memory at that speed is just not feasible in a socket because of the electrical limitations of not having a physically soldered connection. Plus, the physical sizes of GPUs vary quite a bit within the same product stack, so you'd have a choice of either limiting upgradeability to a few GPU models (kinda defeating the purpose) or paying for a bunch of socket area you won't use.

 

Both Intel and AMD did experiment with card-based CPUs in the Pentium II and K7 era-- neither one really caught on. With modern chips, you'd need 15 PCIe x16 slots to match a normal consumer socket's pinout, or 50 x16 slots for a workstation chip like Threadripper.