SDGE motherboards have two PCI Express x16 slots, but one of them is not operational. To enable the second slot, you need to install an add-on card (SDGE card). This add-on card has a chip (HyperTransport tunnel chip) that enables it.
The idea behind this strange concept is to provide a cheap motherboard that you can transform it, in the future, into a SLI or Crossfire motherboard.
Basically, SDGE connects the extra 16x PCI Express slot on the HyperTransport bus. Since the location of this bus on the system depends on the platform, the architecture of SDGE varies depending on the platform. Let’s take a look at how SDGE is built on both AMD and Intel platforms.
ECS gave us a Flash animation showing how this technology works. Click here to watch this animation.
Since socket 754 and socket 939 processors use the HyperTransport bus to communicate with the north bridge, the SDGE card is installed between the CPU and the north bridge chip, as you can see in Figure 2.
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Figure 2: How SDGE works on AMD platform.
The HyperTransport Tunnel chip located on the SDGE card connects the extra 16x PCI Express slot on the HyperTransport bus. The original 16x PCI Express slot continues to be connected to the north bridge chip. As we mentioned both slots work at 16x rate.
Intel CPUs don’t use the HyperTransport bus. However, the link between the north bridge (or MCH, Memory Controller Hub, as Intel calls their north bridge chips) and the south bridge (or ICH, I/O Controller Hub, as Intel calls their south bridge chips) use the HyperTransport bus. So on Intel platform SDGE card is connected between the north bridge and the south bridge link, as you can see in Figure 3.
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Figure 3: How SDGE works on Intel platform.
The funny thing is that, as far as we know, only NVIDIA and ULi chipsets use the HyperTransport bus to connect the north bridge to the south bridge. So, for Intel platform, this technology would be available only on motherboards using chipsets from NVIDIA or ULi - and not for all chipsets like ECS is claiming. Since this is only a concept, we still need to wait for the final product in order to see what they've done. Click here to learn more about this subject.
The HyperTransport Tunnel chip located on the SDGE card connects the extra 16x PCI Express slot on the HyperTransport bus present between the north bridge and the south bridge. The original 16x PCI Express slot continues to be connected to the north bridge chip. As we mentioned both slots work at 16x rate.