Motherboard Design

There are several advantages in using FB-DIMM memories on servers. We have already mentioned two of them: greater memory capacity and higher performance. There is also another great advantage that is the simplification in motherboard design, since the path between the chipset and the memory sockets uses less wires.

Even tough FB-DIMM uses standard DDR2-DIMM sockets, which have 240 pins, it actually uses only 69 of these pins, making it easier to make the motherboard routing (design of the wires on the printed circuit board).

On Figure 2 you can see the necessary routing to connect the north bridge to the DDR2 sockets using just one memory channel. A three-layer printed circuit board is needed.

click to enlarge
Figure 2: DDR2-DIMM routing, one channel.

Now on Figure 3 you can see the necessary routing to connect the north bridge to the FB-DIMM sockets using two channels. It not only uses fewer wires but also uses only two layers from the printed circuit board, making the motherboard simpler to design (the motherboard still needs to use a three-layer PCB; the third layer is used for power wires). Notice FB-DIMM using two channels uses fewer wires than DDR2-DIMM using just one channel.

click to enlarge
Figure 3: FB-DIMM routing, two channels.

Total or partial reproduction of the contents of this site, as well as that of the texts available for downloading, be this in the electronic media, in print, or any other form of distribution, is expressly forbidden. Those who do not comply with these copyright laws will be indicted and punished according to the International Copyrights Law.

We do not take responsibility for material damage of any kind caused by the use of information contained in Hardware Secrets.