There’s tons of senseless discussions and questions and wrong facts on the net about intel QPI and DMI. Here is some nonsense you can find over an over again:
- “Is QPI only temporary?”
- “Lynnfield has QPI! It’s only on die.”
- “intel is moving back from QPI to DMI.”
OK, it’s sooooooo simple:
QPI is used to connect high volume data transfer between two CPUs or between a CPU and a “northbridge”.
The DMI link is a lower data volume transfer connection used to connect a “southbridge” to a “northbridge” or a “southbridge” to a CPU that has all “northbridge” functionalities integrated (memory controller plus PCIE controller).
intel CAN’T(!) move back to DMI, because such a statement doesn’t make any sense:
Bloomfield still has 50% of the northbridge functionalities (the PCIE controllers) left off on a northbridge (the X58 IOH). Therefore it still needs to connect to a “northbridge”. Naturally it does so through a QPI bus.
Lynnfield has and all Sandy Bridges (as it seemes so far) will have all northbridge functionalities integrated. Therefore they only need to connect to a southbridge (the P55, P67 and X68 PCHs). Naturally they do so through a DMI bus.
QPI is a technology to interconnect DIES. There is NO(!) QPI on the Lynnfield die! The integrated connection to the on-die PCIE controller is not QPI but some internal high-bandwidth connection technology.
QPI isn’t temporary either! It’s possible that it’s a temporary issue to use QPI on desktop systems to connect to the X58 IOH, since even the X68 will need to be just a PCH it seems. But QPI will always be the bus that connects the CPUs of multi-CPU systems!
Are these little things so hard to get??