AI Workloads
This machine has four PCIe Gen3 x16 slots connecting directly to two CPUs, resulting in very high performance for up to four GPU cards.
It is rare to find motherboards that expose ALL four PCIe x16 channels on the CPUs (shown above) to external GPUs via four onboard PCIe x16 slots (shown below).
As of 2025-03-01, the prices of GPUs with more than 16GB of VRAM are very expensive, with the above four PCIe x16 slots we can combine:
- 4 cheaper 16GB GPUs to create 1 virtual GPU with 64GB of VRAM
- 3 cheaper 16GB GPUs to create 1 virtual GPU with 48GB of VRAM
- 2 cheaper 16GB GPUs to create 1 virtual GPU with 32GB of VRAM
We are focusing on 16GB GPUs here due to their price/performance ratio as at early 2025, but larger sizes are possible e.g. consumer grade 24GB GPUs can be used to create a 96GB virtual GPU at much lower cost than a GPU that has 96GB VRAM.
Two GPUs
Most modern GPU used at least 8-pin PCIe Power Connectors.
Both Sense A and Sense B pins of a PCIe 8-pin connector needs to be GROUNDED to deliver 150W (reference: Intel).
Built into the machine there are 6 x 6-pin PCIe Power Connectors off 4 x power cables.
The 6-pin connectors (up to 75W) are not suitable for GPUs needing higher power draw e.g. from 8-pin PCIe Power Connectors (up to 150W).
We can remove the 6-pin to 8-pin adapters on power cable 1 and power cable 2 to expose the higher powered 8-pin connectors.
Below is the result (with two Nvidia GPUs needing 8-pin PCIe power cables and one AMD GPU using power from the PCIe slot only):
Three GPUs
A third dual-slot GPU can be installed by removing the dual 10Gb ethernet card and moving the AMD GPU to its slot. The third dual-slot GPU can then take the place of AMD GPU.
Y-Cable
The machine has two 6-pin PCIe power cables which can be used to power the THRID GPU using a "Dual 6-pin Female to Single 8-pin Male PCIe Power Y-cable".
The above shows how the power from 2 x 6-pin connectors are combined, "ground" is connected to the second sense pin (green) of the 8-pin connector to deliver 150W.
Note the 3rd Nvidia GPU can reduce the air-flow to the AMD GPU substantially, so unless the AMD GPU can be replaced with a fanless GPU this is not a good solution.
Four GPUs
Four dual-slot GPUs will NOT fit into the case, so we need to add riser cables as well as external power supply.
In order to fit 4 dual-slot GPUs into the case, riser cables are needed.
Photo above shows 2 riser cables plugged into the GPU3 and GPU4 PCIe x16 slots.
Secondary Power Supply
When buying a new secondary power supply for the four GPUs, it should be of modular design (no pre-attached cable) and should have at least:
- 4 x PCIe 8-pin (150W each) output ports
If a high power GPU is needed then the power supply should also have at least:
- 1 x PCIe 5.1 (600W) output port
Examples:
You can purchase a small relay to switch the secondary power supply ON and OFF the same time as the primary power supply.
